The MV Smyrtos Interdiction: Can Stateless Vessels on the High Seas be Seized and the Crew Prosecuted?

[Thea Coventry is a PhD candidate in international law and adjunct lecturer at Leiden University, specialising in maritime security, transnational criminal law and state jurisdiction.]

Since 2025, the number of stateless and falsely flagged vessels transporting sanctioned Russian oil through the North and Baltic Seas has almost quadrupled. In June 2025, in response to this development, the Nordic-Baltic 8++ States announced coordinated action against vessels used to circumvent sanctions on Russian crude oil. In a joint statement, the States asserted that vessels without a flag are not entitled to rights under UNCLOS, including freedom of navigation. They further indicated that they would ‘take appropriate action within international law’ if a vessel fails to fly a valid flag while transiting through the North and Baltic Seas.

Although several European States have detained stateless oil tankers and imposed penalties before ultimately releasing them, the United Kingdom has recently taken a different approach in enforcing sanctions against the Russian shadow fleet. On 14 June 2026, for example, the United Kingdom conducted its first solo interdiction of a sanctioned oil tanker suspected of falsely flying the Cameroon flag despite having been expelled from the country’s registry in May. Royal Marine Commandos and specialised law enforcement officers boarded the oil tanker MV Smyrtos as it sailed through the English Channel. The tanker was carrying more than 100,000 tonnes of Russian crude oil. Notably, the captain, an Indian national, was arrested and charged with allegedly controlling a ship delivering prohibited oil or oil products from Russia to a third country.

The United Kingdom justified the interdiction by reference to Article 110 UNCLOS and domestic law. According to the Ministry of Defence, ‘where a vessel is determined stateless, the UK can exercise powers available under its domestic legislation’. Although initial government press releases stated that the vessel was boarded on the high seas, subsequent information asserted that it had voluntarily entered UK waters. Yet international law is far from clear about whether States may seize stateless vessels on the high seas and prosecute their crew for domestic sanctions evasion offences in the absence of an internationally recognised basis of prescriptive jurisdiction.

Boarding and Seizing Stateless Vessels

The legal basis for boarding and detention of the Smyrtos depends upon the location of the vessel. If the vessel is on the high seas, the relevant enforcement powers are set out in Part VII of UNCLOS. Article 110 of UNCLOS permits States to stop and board, and where necessary search, a vessel that is suspected of being without nationality or sailing under the flag of two or more States interchangeably. False-flag activity, such as falsely claiming a nationality or repeatedly switching flags, may give rise to a suspicion of statelessness and thus justify the exercise of the right of visit. However, UNCLOS does not expressly authorise any further enforcement action against stateless vessels, cargo or crew, such as seizure and arrest. This gap reflects broader uncertainties in the law of the sea concerning the definition, status and legal consequences of stateless vessels.

UNCLOS uses but does not define the term ‘ship without nationality’, mentioned in Article 92(2), nor does it establish an international test for determining a ship’s nationality. This leaves unclear which vessels are without nationality, as distinct from merely unregistered or unflagged. Although it requires States to maintain registers for ships above a certain size (Article 94(2)(a)), UNCLOS leaves the conditions for granting nationality to ships to the domestic law of each State (Article 91). States traditionally apply different criteria, such as the nationality of the owner or place of construction.

A State can also recognise a vessel as possessing its nationality without requiring registration. Thus, the mere fact that a vessel is not registered does not ipso facto render it stateless. Nevertheless, where a vessel’s nationality is disputed, the claimed nationality should be supported by documentary or other reliable evidence demonstrating that the purported flag State had recognised the vessel as possessing its nationality prior to the incident (Article 91(2)). Such evidence is important to prevent a State from asserting retrospectively, after an incident, that it had always regarded the vessel as possessing its nationality.

UNCLOS is similarly unclear as to the legal status of a vessel that is found to be without nationality. The Convention does not expressly require every vessel to possess a nationality, nor does it expressly prohibit stateless vessels from navigating the high seas. While Article 92(2) addresses vessels sailing under two or more flags interchangeably, providing that such vessels may not claim any of the nationalities concerned, it does not specify what consequences follow where a vessel is left without a nationality. Nor does Article 110, which permits States to stop and search a vessel suspected of being without nationality, determine what further action may be taken once its statelessness is established.

The legal consequences of statelessness are therefore unsettled. One position, reflected in a statement by the Nordic-Baltic 8++ States, is that stateless vessels are not entitled to rights under UNCLOS, including freedom of navigation. Thus, some scholars have argued that stateless vessels may be escorted to port while their status and ownership are further investigated. However, this exclusion from freedom of navigation cannot be inferred merely from the non-registration of smaller vessels. As the Arbitral Tribunal in Enrica Lexie clarified, as UNCLOS does not require all ocean-going vessels to be registered, States may therefore ‘exceptionally, exercise their freedoms under Article 87 of the Convention also through small non-registered vessels’.

A more expansive view is that the absence of a flag State leaves the vessel without the protection of any State and permits other States to apply their domestic laws to the vessel and those on board, including through enforcement jurisdiction. This position reflects a historical strand of scholarship that treated vessels without nationality as outlaws on the high seas and assimilated them to pirates. Under this approach, the absence of nationality provides a basis for enforcement measures extending beyond the inspection authorised by Article 110, potentially including detention, seizure and the exercise of criminal jurisdiction. The assimilation of stateless vessels to piracy is, however, contested (see also here). While sailing without a flag might historically have given rise to a suspicion of piracy, sailing a vessel without nationality is not itself an international crime.

The legal consequences of statelessness therefore remain unsettled. Different views have been advanced as to whether statelessness affects a vessel’s ability to navigate the high seas, deprives it of the rights associated with a flag State, or permits other States to exercise broader enforcement or criminal jurisdiction in the absence of a flag State. The precise consequences are important to the legality of any action taken against the Smyrtos beyond the initial boarding and search.

Prescribing High Seas Offences and Prosecuting Seafarers 

The prosecution of the Indian captain of the Smyrtos raises a specific issue related to prescriptive jurisdiction. Regardless of whether stateless vessels may legally navigate the high seas or not, boarding States may not take high seas enforcement action beyond Article 110 unless the boarding State can establish an additional legal basis for seizure and prosecution. Thus, the lawfulness of the prosecution of the Smyrtos’ captain depends on whether the conduct falls within the scope of the relevant UK criminal law and whether international law permits States to extend their criminal jurisdiction to stateless vessels on the high seas,

The captain of the Smyrtos was charged pursuant to Regulation 46Z9B of The Russian (Sanctions)(EU Exit) Regulations 2019. This regulation applies only to conduct performed within UK territory and territorial sea, as well as UK persons abroad. According to the prosecutor, the vessel was seized after it had ‘entered UK territorial waters without a legitimate flag’. Yet initial government press releases stated that the vessel had been boarded on the high seas (also here). If the vessel was in fact boarded beyond UK territorial waters, then the UK would not have prescriptive jurisdiction as a matter of its domestic law, as the Regulations do not extend to conduct performed by foreign nationals aboard stateless vessels on the high seas.

Leaving this issue of domestic jurisdiction aside, the question remains whether the UK can prosecute the Indian captain of the Smyrtos as a matter of international law. Under the prevailing view, States may only exercise prescriptive jurisdiction on recognised bases, including territorial and flag State jurisdiction, active and passive nationality, the protective principle and universal jurisdiction. If the Smyrtos had not entered UK waters before boarding, then prosecuting the Indian captain for conduct occurring aboard a stateless vessel on the high seas would therefore require the UK to rely on universal jurisdiction. However, the delivery of Russian oil products falls beyond the generally accepted scope of the principle, thus presumptively rendering the United Kingdom’s act in prosecuting an Indian national unlawful under international law.

Nevertheless, the extension of universal jurisdiction to sanctions evasion is permissible under an alternative account of state jurisdiction under international law. While State practice generally limits universal jurisdiction to a narrow category of serious international crimes, it can be argued that this list is illustrative of State practice rather than an exhaustive rule of international law. Instead, according to this alternative account, States may assert universal jurisdiction over serious extraterritorial offences, provided that the domestic criminalisation does not interfere with the public order of other States. Arguably, conduct occurring aboard stateless vessels falls outside the public order of other States because no flag State has exclusive jurisdiction to regulate conduct aboard the vessel. Thus, while stateless vessels should not be considered ipso facto pirate vessels, they could fall within an analogous category of vessels subject to universal jurisdiction under international law.  

Conclusion

The increasing use of stateless and falsely flagged vessels to transport sanctioned Russian oil has exposed a jurisdictional gap between flag State jurisdiction, coastal State jurisdiction, and domestic sanctions regimes. As coastal State jurisdiction generally ends at the territorial sea and sanctions regimes are typically tied to territorial or nationality-based jurisdiction, stateless vessels can fall outside the jurisdiction that would ordinarily regulate conduct at sea.

The Smyrtos illustrates the difficulties that this jurisdictional gap creates. While Article 110 provides a clear basis for boarding vessels, such as the Smyrtos, where there is a suspicion that the vessel is without nationality on the high seas, it is much less clear whether UNCLOS authorises further enforcement action beyond boarding and inspection. Moreover, even if there is no bar to maritime enforcement under international law, that does not automatically establish prescriptive jurisdiction over the conduct of foreign seafarers on the high seas. The lawfulness of the prosecution of the Smyrtos’ captain therefore depends on both the factual location of the vessel and the domestic and international basis for applying UK sanctions law to his conduct.  

States nevertheless have a legitimate interest in preventing stateless vessels from becoming vehicles for sanctions evasion. Given the position of stateless vessels under international law remains unsettled, repeated State interdictions, accompanied by legal statements asserting their validly under international law, may contribute to the development of a customary rule permitting broader criminal jurisdiction over stateless vessels, analogous to that applicable to piracy. Silence by other States may support an inference of acquiescence, whereas repeated diplomatic protest would indicate opposition to a general enforcement power over stateless vessels on the high seas. In light of this uncertainty, States should also work through appropriate international fora to develop clearer international rules defining when stateless vessels may be subjected to enforcement, together with safeguards for the prosecution of seafarers for conduct occurring on the high seas. 

Photo attribution: Photo by Shaah Shahidh on Unsplash