kerch strait case, itlos

this is an analysis paper I wrote at the beginning of 2022, as part of a Sant’Anna course on the obligation to solve disputes through peaceful means in international law.

this is to say: I was under no obligation to focus on this (very) specific tribunal, procedure, or case. I picked this topic in mid-January of 2022 and turned in the finished paper at the end of March 2022, writing and revising it during the first few weeks of Russia’s war of aggression on Ukraine.

to this day, I count it amongst my own favourite writing samples, even though it feels, in a way, almost too simple; but it was clear, concise and, sadly, extremely timely.

the following text hasn’t been edited since then, except for small non substantial corrections.

Case concerning the detention of three Ukrainian naval vessels (Ukraine v. Russian Federation), Provisional Measures”: ITLOS Case No. 26, Kerch Strait incident


On November 25th, 2018, in the vicinity of the Kerch Strait, the Russian Federal Security Service Coast Guard arrested and detained three Ukrainian vessels – the Berdyansk and the Nikopol, warships, and the Yani Kapu, an auxiliary vessel – as well as the twenty-four Ukrainian servicemen on board.

While sailing from the port of Odesa towards Berdyansk, the Ukrainian vessels had received communications by the Russian Coast Guard asserting the Strait was closed. The vessels had briefly proceeded towards the strait, only to be blocked, pursued, and ultimately arrested by the Russian Coast Guard while travelling away from the Crimean coastline. The vessels were seized and led to the Russian-occupied port of Kerch, where they were held as evidence in the trial against the servicemen. The latter were apprehended and detained in the Lefortovo Prison in Moscow as suspects for the crime of aggravated illegal crossing of the State border of the Russian Federation, in accordance with Section 3, Article 322, of the Criminal Code of the Russian Federation. At the time of the request for provisional measures, Russian courts had twice renewed the detention of crewmen and vessels while investigating the incident.

Exactly three years ago, on March 31st, 2019, Ukraine instituted arbitral proceedings against the Russian Federation, concerning the facts outlined above. Pending the constitution of the arbitral tribunal, after two weeks, Ukraine submitted a request for the prescription of provisional measures to the International Tribunal for the Law of the Sea (ITLOS). On April 30th, the Russian Federation notified the tribunal of its decision not to participate in the case hearing, later transmitting a memorandum clarifying its position on the case. Oral statements were presented by Ukraine’s delegation on May 10th, along with the final submissions containing the requested provisional measures. The tribunal delivered its Order on May 25th.

Foundation of the dispute under International Law

The immunity of warships is a core sovereign immunity: warships and their personnel cannot be arrested by the law enforcement authorities of foreign States, subjected to the jurisdiction of foreign courts, seized, arrested, or detained by any legal means [1]. This constitutes customary international law by nature of consistent practice and unanimous opinio juris.

The incident occurred in Ukraine’s territorial sea or exclusive economic zone [2], but Ukraine argues that Russia’s actions would still constitute a violation of the Convention had they occurred in Russia’s territorial sea or exclusive economic zone. If a warship does not comply with the coastal State’s law applicable to passage through the territorial sea and disregards requests for compliance, the State may only require it to leave the territorial sea immediately ex UNCLOS Art 30. In this case, even though the Ukrainian vessels were already leaving the area, Russian forces seized them and arrested the crew, subjecting them to Russian jurisdiction.

Before ITLOS, Ukraine was then requesting provisional measures to counter the seizure of the ships and the detention of its seamen based on UNCLOS Art 290(5), which reads:

Pending the constitution of an arbitral tribunal to which a dispute is being submitted under this section, any court or tribunal agreed upon by the parties or, failing such agreement within two weeks from the date of the request for provisional measures, the International Tribunal for the Law of the Sea […] may prescribe, modify or revoke provisional measures in accordance with this article if it considers that prima facie the tribunal which is to be constituted would have jurisdiction and that the urgency of the situation so requires […].The doctrine has recognized the “revolutionary” character of this article, which has the Tribunal prescribing rather than indicating said measures [3], reinforced in Art 290(6) by the obligation for parties to conform to provisional measures. Both the Russian Federation and Ukraine have ratified UNCLOS, apposing declarations that will be mentioned below where relevant.

Prima facie jurisdiction

In order to establish jurisdiction ex UNCLOS Art 288(1), the Tribunal first had to assess whether, on the date of the institution of arbitral proceedings, a dispute concerning the interpretation or application of the Convention existed between the Parties. Ukraine argued that the Parties were clearly engaged in such a dispute, specifically concerning UNCLOS Art 30 and warship immunity, and that the Annex VII tribunal had the competence to resolve this divergence. ITLOS held the view that since Russian authorities arrested and detained the Ukrainian naval vessels and commenced criminal proceedings against the Ukrainian servicemen, the Russian Federation must have held a different position from Ukraine on the question of whether the “Kerch Strait Incident” had given rise to the alleged breach of its obligations under UNCLOS Artt 32, 58, 95 and 96. The Tribunal therefore considered that a dispute concerning the interpretation or application of the Convention prima facie appeared to have existed on the date the arbitral proceedings were instituted.

ITLOS noted that the Russian Federation had denied the “categorisation of the situation as an armed conflict for the purposes of international humanitarian law”. However, the Russian thesis against ITLOS jurisdiction in this case rested on the exception detailed under UNCLOS Art 298(1)(b) for disputes concerning military activities. Indeed, upon ratification of the Convention, both parties had declared that they would not accept procedures entailing binding decisions, such as the one deriving from Art 290(5), with respect to disputes concerning military activities. Although both parties made very similar declarations, in this instance they disagreed on the nature of the incident, with Ukraine claiming that the Russian response constituted a police operation short of military confrontation, and the Russian Federation insisting that it constituted military activity. According to the Russians, the involvement of military vessels was sufficient to imply military activity, especially considering the allegedly aggressive and secretive behaviour of the Ukrainians. The opposing argument instead rested on the fact that the alleged UNCLOS violation was not military in nature but connected to Russia’s unlawfully exercising jurisdiction on Ukrainian warships in a law-enforcement context. The tribunal here sided with Ukraine in considering the nature of the actions undertaken, rather than the status of the vessels involved, as the primary factor to determine the applicability of the military activity exception. The tribunal asserted that transit of warships does not automatically constitute military activity, especially since the confrontation was caused by the Parties’ differing interpretation of the regime of passage through the Kerch Strait. The use of force during the incident itself was also coherent with a law enforcement operation.

The Tribunal also found it appropriate to assess whether the requirements under Art 283(1) [4], concerning the exchange of views between parties, had been met. The Russian Federation, indeed, contended that it had not been satisfied and that Ukraine had arbitrarily imposed deadlines, truncating the negotiation process. Both Parties maintained that they had not found the other’s full collaboration to the resolution of the dispute. ITLOS found that “a State Party is not obliged to continue with an exchange of views when it concludes that the possibilities of reaching agreement have been exhausted” [5] and that “the obligation to proceed expeditiously to an exchange of views applies equally to both parties to the dispute”[6]. After analysing the epistolary exchanges and the related meetings, it found Ukraine had complied with Art 283(1).

Provisional measures

Having established prima facie jurisdiction, at this stage of the proceedings, the tribunal had to assess whether the rights that Ukraine sought to protect could be considered at least “plausible” [7]. The Tribunal considers that the rights claimed by Ukraine concerning the immunity of warships and auxiliary vessels on the basis of UNCLOS Artt 32, 58, 95 and 96, as well as those concerning the immunity of the twenty-four servicemen, were plausible under the circumstances, although the latter were considered potentially deserving of further scrutiny. The requirement of plausibility of the protected rights, however, was deemed fully satisfied.

According to Ukraine, the detention of warships and crew was an interference on its sovereignty, preventing the conduction of public duties, while impeding maintenance of the vessels, potentially causing extended or permanent loss of their seaworthiness. By detaining the vessels, the Russian Federation had also gained access to “highly sensitive equipment including instruments, arms on board, and equipment intended to provide secure communications between the vessel and its command”, which was “crucial to Ukraine’s defence”. Finally, the detention of the servicemen entailed irreparable prejudice to their individual rights. Ukraine asserted that the risk of irreparable prejudice was not just imminent but already under way, and the harm imposed on its vessels and servicemen increased with the passing of each day, making the situation “exceptionally urgent”. In Ukraine’s view, harm of this nature could not be remedied by an award of damages and the Tribunal’s position aligned with Ukraine’s.

The requested provisional measures would require the Russian Federation to promptly: release the three Ukrainian naval vessels and return them to the custody of Ukraine; suspend criminal proceedings against the 24 detained Ukrainian servicemen and refrain from initiating new proceedings; and release the servicemen to allow them to return to Ukraine. The Russian Federation argued that doing so would remove any possibility of it exercising its rights since the vessels and crew would no longer be subject to its jurisdiction, and that Ukraine’s request for provisional measures coincided with its requests on the merits, thus prejudging them.

ITLOS Order and additional opinions

The Tribunal countered the Russian argument that the Order would prejudge the matter of jurisdiction of the Annex VII tribunal or deal with the merits of the case. It also noted that, in accordance with Art 89(5), of its Rules, it may prescribe measures different in whole or in part from those requested.

Considering relevant ITLOS precedent, the Tribunal previously issued orders included measures: precluding judicial or administrative measures against the master, crew, owners and operators of an oil tanker, even after that vessel’s release from detention by the coastal State (M/V Saiga); requiring the release on bond of a vessel and all detained passengers and crew members (Arctic Sunrise); and requiring the suspension of all court proceedings against Italian marines accused of killing two Indian fishermen while on board an oil tanker (Enrica Lexie). Ukraine claimed that the detention of its warships presented a categorically different, more serious, and more urgent situation than those presented in the aforementioned cases.

In its Order, ITLOS considered it appropriate to require the Russian Federation to release the three Ukrainian naval vessels and the twenty-four detained Ukrainian servicemen and to allow them to return to Ukraine, in order to preserve the rights claimed by Ukraine. It did not consider it necessary to require the Russian Federation to suspend criminal proceedings against the twenty-four detained Ukrainian servicemen.

Six judges produced additional opinions. The declaration of Judge Kittichaisaree was meant to further explain the reasoning behind the Tribunal’s Order, pointing out that the choice not to prescribe the interruption of Russian court proceedings has not been justified. It also contained a further analysis of the requirement to an expeditious exchange of views, as well as an alternative justification for the immunity of the servicemen onboard. Judge Kittichaisaree also clarified that since Russia did not seem to accept that there was a situation of armed conflict between Russia and Ukraine, ITLOS could not apply the law of naval warfare as lex specialis to allow the targeting of military objectives such as enemy warships to achieve a military advantage. The declaration of Judge Lijnzaad expressed reservations with regards to the considerations on applicable law, especially because of the potential involvement of other rules of international law, such as the law of conflict, that are outside the jurisdiction of ITLOS.

The separate opinion of Judge Jesus did not counter the position or the arguments outlined in the Order, but rather gave further thought on the issue of the characterization of the conduct of Ukraine’s vessels as military activity, finding it not to be correct on the basis of available information. The separate opinion of Judge Lucky asserted that the tribunal exercised fairness even though the Russian Federation did not participate in the proceedings. Judge Lucky agreed with the decision not to suspend criminal proceedings in Russia, but only on the basis that the Tribunal did not have jurisdiction to interrupt judicial proceedings in a sovereign country. In his separate opinion, Judge Gao asserted that he agreed with the final judgement to uphold the longstanding principle of immunity of warships; however, he expressed “major reservations” on the approach to the issue of military activities exception, as raising the threshold for military activity might incentivize States to escalate conflicts in order to qualify for such exceptions.

The dissenting opinion of Judge Kolodkin was wholly based on the opinion that the military activities exception did apply in the case at hand, and therefore ITLOS lacked jurisdiction.

Compliance and aftermath

Pursuant to article 95, paragraph 1, of the Rules of the Tribunal, each party is required to submit to the Tribunal a report and information on compliance with any provisional measures prescribed. The Tribunal reaffirmed that the non-appearing party is nevertheless a party to the proceedings [8], with the ensuing rights and obligations, including an obligation to comply with any provisional measures prescribed under UNCLOS Art 290.

On June 25th, Ukraine filed a report stating that the Russian Federation had not complied with the provisional measures set forth in the Tribunal’s Order, while the Russian Federation reported to ITLOS that they would propose to Ukraine “specific procedural measures” to allow for the release of crewmen and vessels. On June 26th, Ukraine supplemented its previous report attaching a note verbale from the Russian Federation, requesting guarantees that the servicemen would participate in the investigation upon their release. In presenting this document to ITLOS, Ukraine noted that the request for guarantees went against the Order, further aggravating the dispute. This marks the end of the public case documents.

The twenty-four servicemembers were returned to Ukraine on September 7th, as part of a prisoner exchange [9]. The three vessels were finally returned on November 18th, in what could be interpreted as a goodwill gesture ahead of a peace summit on eastern Ukraine in December 2019 [10].

Conclusions. Evaluation of the choice of peaceful resolution mechanism

Judicial settlement is one of the peaceful means of resolution of international disputes outlined in Art 33 of the United Nations Charter. In the case outlined, given that unstructured negotiation was not sufficient to solve the dispute, Ukraine followed the procedure outlined in UNCLOS, an international Convention that both States involved in the controversy are part of. After instituting arbitral proceedings ex Annex VII of the Convention, pending the constitution of the arbitral tribunal, after two weeks – as per the procedure prescribed in Unclos Art 290(5) – Ukraine submitted to the Tribunal the request for provisional measures discussed above. This procedure ran parallel to a series of other avenues for relief, such as the original arbitral proceedings, a request for interim measures brought before the European Court of Human Rights, a statement before the UN Security Council[11], an official statement before the OSCE[12].

Still, the recourse to ITLOS was particularly suited to the case at hand, as it provided for compulsory provisional measures on the basis of a well-established international consuetudinary law principle. By briefly touching upon other means of dispute resolution, it will hopefully be clear that none of them would have been appropriate to the case at hand.

Negotiation is a powerful and flexible tool for conflict resolution, but it requires a basis of good faith between the parties. Without invalidating Ukraine’s position that the Kerch Strait incident constituted a law-enforcement operation rather than military activity, it is indisputable that the relationship between the Parties at the time was not friendly. In fact, the “Kerch Strait Incident” can be considered as the first time Russia openly recognized engaging with Ukrainian forces after the beginning of the ongoing Russo-Ukrainian conflict. Therefore, taking into account the historical context in addition to legal considerations, it appears clear that negotiations would have been unlikely to work. The documentation submitted before ITLOS in this case further supports this argument, as it is clear that both Parties harboured doubts regarding the intentions of the other while fulfilling their obligation to exchange views under UNCLOS Art 283.

The conduction of an international enquiry would not have led to a resolution of this case. Most of the factual elements in this case were clear and undisputed by the Parties, and the few unclear details were not relevant to the legal argument brought forward by Ukraine. The dispute did not concern the events of November 25th, 2018, but rather the well-documented actions undertaken by one of the Parties in response to such events and the compliance of this response with international customary law. UNCLOS Annex VIII Art 5(2) details a special fact-finding procedure, the results of which are binding unless otherwise agreed; but its fields of applications are limited, and again, it would not have solved the central matter of the dispute.

Conciliation is foreseen by UNCLOS Art. 284 as a potential dispute resolution procedure and disciplined in UNCLOS Annex V. Unfortunately, as its recommendations are not binding, it is an ill-suited solution for the dispute at hand, where the two parties are both highly motivated in the defence of their respective position. Even though the recommendations could be used as relevant material to institute further proceedings, as the case made by Ukraine is quite clear-cut, such a procedure would be little more than a waste of time. The same applies to good offices, which in addition are not explicitly foreseen or disciplined by UNCLOS.

While it is not possible to exclude that any attempts at mediation have taken place, as such procedures are often not public, considering the development of this case as well as the historical context between the Parties, such an avenue would have been largely ineffective.

As for the possibility to resort to regional agencies, the identity of one of the Parties – the Russian Federation – blocked the way of a potential binding United Nations Security Council Resolution. The discussion in that forum of a letter sent by the Permanent Representative of Ukraine detailing the incident[13] confirmed the utter disregard by the Russian Federation of the possibility of a peaceful resolution of this dispute through diplomatic means. Other regional organisations, such as the OSCE, are not binding in nature, and therefore would not have been able to drastically influence the process of resolution of this dispute.

The two peaceful avenues that remained available were then arbitration and judicial settlement. It is not a coincidence that they are the only two options that produce legally binding results. Ukraine instituted arbitral proceedings under UNCLOS Annex VII and moved forward with the request for provisional measures examined here after two weeks, considering this to be a time-sensitive issue.

On the other hand, Russia’s choice not to participate to the case hearing is coherent with its thesis, but ultimately conducive to an Order contrary to its position. The Russian Federation maintained that compulsory dispute resolution procedures under UNCLOS could not apply to this case because of the declaration made excluding military activity disputes from such procedures. Still, it complied with the Order, although perhaps in a less than prompt manner. In truth, the lack of an enforcement mechanism would not have given rise to any direct consequences for non-compliance. However, in previous ITLOS cases relating to international disputes over the arrest, detention, and release of vessels, all the parties concerned complied with the decisions rendered by the Tribunal. In this case, too, the Russian Federation ended up complying with the ITLOS Order; had it not done so, Ukraine might have attempted to move forward with a United Nations General Assembly Resolution, but that option would have been non-binding and therefore potentially ineffective.

The case of the “Kerch Strait Incident” acquires further relevance in hindsight, as it constitutes the first direct engagement of Ukrainian forces by the Russian Federation during the ongoing Russo-Ukrainian conflict. In this context, it showcases Ukraine’s attempt to peacefully solve the international controversy that had arisen and the Russian Federation’s continued attempts to avoid upholding international law principles whenever convenient.


[1] “Les bâtiments militaires ne peuvent pas être l’objet de saisie, d’arrêt ou de détention par une mesure de justice quelconque ni d’aucune procédure judiciaire in rem”, Institut de Droit International, Travaux préparatoires de la session de Stockholm, Art. 26. Annuaire, 1928. Trad. in de Guttry, 1994. This formula also appears almost identical to its equivalent present in the International Convention for the Unification of Certain Rules relating to the Immunity of State-owned Vessels, signed in Brussels on April 10th, 1926.

[2] According to Ukraine, “Ukraine does not have precise coordinates for the boarding of the vessels, either because the vessels did not have the opportunity to transmit their position or because the Russian Federation jammed the relevant transmissions.”

[3] The Statute of the International Court of Justice only allows it to “indicate” provisional measures ex Art 41.

[4] UNCLOS Art 283(1) reads: “When a dispute arises between States Parties concerning the interpretation or application of this Convention, the parties to the dispute shall proceed expeditiously to an exchange of views regarding its settlement by negotiation or other peaceful means.”

[5] Cases cited: MOX Plant (Ireland v. United Kingdom), Provisional Measures, Order of 3 December 2001, ITLOS Reports 2001, p. 95, at p. 107, para. 60; “ARA Libertad” (Argentina v. Ghana), Provisional Measures, Order of 15 December 2012, ITLOS Reports 2012, p. 332, at p. 345, para. 71; “Arctic Sunrise” (Kingdom of the Netherlands v. Russian Federation), Provisional Measures, Order of 22 November 2013, ITLOS Reports 2013, p. 230, at p. 248, para. 76.

[6] Cases cited: M/V “Norstar” (Panama v. Italy), Preliminary Objections, Judgment, ITLOS Reports 2016, p. 44, at p. 91, para. 213

[7] “At this stage of the proceedings, the Tribunal is not called upon to determine definitively whether the rights claimed by Ukraine exist, but need only decide whether such rights are plausible”. ITLOS Orders cited: “Enrica Lexie” (Italy v. India), Provisional Measures, Order of 24 August 2015, ITLOS Reports 2015, p. 182, at p. 197, para. 84; Delimitation of the Maritime Boundary in the Atlantic Ocean (Ghana/Côte d’Ivoire), Provisional Measures, Order of 25 April 2015, ITLOS Reports 2015, p. 146, at p. 158, para. 58.

[8] Cases cited: Nuclear Tests (Australia v. France), Interim Protection, Order of 22 June 1973, I.C.J. Reports 1973, p. 99, at pp. 103–104, para. 24; “Arctic Sunrise” (Kingdom of the Netherlands v. Russian Federation), Provisional Measures, Order of 22 November 2013, ITLOS Reports 2013, p. 230, at p. 242, para. 51.

[9] CNN, Film director Oleg Sentsov and MH17 suspect among those freed in Russia-Ukraine prisoner swap, 2019

[10] Reuters, Ukraine confirms Russia returning three captured naval ships, 2018

[11] UNSC, 8410th meeting, November 26th, 2018

[12] Statement by H.E. Mr. Pavlo Klimkin, Minister for Foreign Affairs of Ukraine, at the 25th Meeting of the Ministerial Council of the OSCE (2018)

[13] UNSC, 8410th meeting, November 26th, 2018


Case documents

  • Request of Ukraine for the prescription of Provisional measures under Article 290, paragraph 5, of the United Nations Convention on the Law of the Sea, April 16th, 2019 [retrieved here]
  • Note verbale of the Embassy of the Russian Federation in the Federal Republic of Germany, April 30th, 2019 [retrieved here]
  • Letter of the Agent of Ukraine, May 2nd, 2019 [retrieved here]
  • Memorandum of the Government of the Russian Federation, May 7th, 2019 [retrieved here]
  • Minutes of the public sitting held on May 10th, 2019 [retrieved here]
  • Final submissions of Ukraine, May 10th, 2019 [retrieved here]
  • ITLOS Order 2019/1 of April 23rd, 2019 [retrieved here]
  • ITLOS Order 2019/2 of May 2nd, 2019 [retrieved here]
  • ITLOS Order May 25th, 2019 [retrieved here]
  • Declaration of Judge Kittichaisaree [retrieved here]
  • Declaration of Judge Lijnzaad [retrieved here]
  • Separate Opinion of Judge Jesus [retrieved here]
  • Separate Opinion of Judge Lucky [retrieved here]
  • Separate Opinion of Judge Gao [retrieved here]
  • Dissenting Opinion of Judge Kolodkin [retrieved here]
  • Report of Ukraine of June 25th 2019 [retrieved here]
  • Report of the Russian Federation of June 25th 2019 [retrieved here]
  • Supplementary report of Ukraine of June 26th 2019 [retrieved here]

Cases cited

  • Nuclear Tests (Australia v. France), 1973 (ICJ)
  • MOX Plant (Ireland v. United Kingdom), 2001 (ITLOS)
  • ARA Libertad” (Argentina v. Ghana), 2012 (ITLOS)
  • “Arctic Sunrise” (Kingdom of the Netherlands v. Russian Federation), 2013 (ITLOS)
  • “Enrica Lexie” (Italy v. India), 2015 (ITLOS)
  • Delimitation of the Maritime Boundary in the Atlantic Ocean (Ghana/Côte d’Ivoire), 2015 (ITLOS)
  • M/V “Norstar” (Panama v. Italy), 2016 (ITLOS)

Select bibliography

  • Churchill, R., ‘Compulsory’ Dispute Settlement under the United Nations Convention on the Law of the Sea – How has it operated? Pt. 1. PluriCourts, 2016 [retrieved here]
  • CNN, Film director Oleg Sentsov and MH17 suspect among those freed in Russia-Ukraine prisoner swap, 2019 [retrieved here]
  • de Guttry A., Lo status delle navi da guerra italiane in tempo di pace ed in situazione di crisi, 1994
  • Institut de Droit International, Travaux préparatoires de la session de Stockholm, Annuaire [retrieved here]
  • International Convention for the Unification of Certain Rules relating to the Immunity of State-owned Vessels, 1926
  • Phan, H.D., International Courts and State Compliance: An Investigation of the Law of the Sea Cases. Ocean Development & International Law, 2018
  • Reuters, Ukraine confirms Russia returning three captured naval ships, 2018 [retrieved here]
  • Schatz, V.J., Koval, D. Ukraine v. Russia: Passage through Kerch Strait and the Sea of Azov, Völkerrechtsblog, 2018 [retrieved here]
  • Statement by H.E. Mr. Pavlo Klimkin, Minister for Foreign Affairs of Ukraine, at the 25th Meeting of the Ministerial Council of the OSCE (2018) [retrieved here]
  • Statute of the International Court of Justice, 1945
  • UN Charter, 1945
  • UNCLOS, 1982 [retrieved here, with declarations]
  • UNSC, 8410th meeting, November 26th, 2018 [retrieved here]
  • Virzo R., Il regolamento delle controversie nel diritto del mare: rapporti tra procedimenti, 2008