Baltic Backdrop: Sanctions Evasion and the Legal Limits of Maritime Enforcement

[Mr Mark Douglas is a Maritime Domain Analyst at Starboard Maritime Intelligence. He qualified as a Marine Engineer Officer while in the Royal New Zealand Navy. He later concurrently served as New Zealand Assistant Defence Advisor to Singapore and the New Zealand International Liaison Officer to the Singapore Information Fusion Centre.

Dr Trung Nguyen is a Research Fellow at the Centre for International Law, National University of Singapore. He previously worked as a legal officer in the Ministry of Foreign Affairs of Viet Nam, working in the law of the sea and ocean policy.]

This post examines recent incidents in the Baltic Sea involving Russia’s shadow fleet, focusing on the legal and geopolitical tensions sparked by tankers evading sanctions and the law of the sea. It critically examines Estonia’s assertive maritime enforcement measures in the Gulf of Finland, situating them within the framework of the United Nations Convention on the Law of the Sea (UNCLOS) and the evolving discourse on the limits of coastal State jurisdiction. The Baltic situation illustrates broader global challenges to maritime law posed by substandard shipping and strategic ambiguity.     

Background to the Problem

In May 2025, a small number of ageing tankers began transforming the Baltic Sea into a crucible of maritime law, regional enforcement, and geopolitical ambiguity. These uninsured, questionably flagged tankers — part of Russia’s ‘shadow fleet’ — are used to evade sanctions and export oil.

Their activities have grown more visible in the Gulf of Finland, a narrow body of water bordered by Russia to the east, Finland to the north, and Estonia to the south. Notable among them are the tankers FALCON, KIWALA, and JAGUAR (renamed BLINT). These ships have demonstrated a pattern of broadcasting spoofed Automatic Identification System (AIS) positions, loitering near sensitive undersea infrastructure, and ignoring radio calls from coastal authorities. The situation came to a head on 13 May 2025 when Estonia challenged, and then escorted JAGUAR out of its waters prompting a Russian fighter jet to enter Estonian airspace.

Estonia’s assertive posture has put the spotlight on a significant legal design: the deliberate shaping of the maritime boundaries in the Gulf of Finland. Both Estonia and Finland agreed to limit the breadth of their territorial seas in the Gulf to 3 nm, instead of the maximum of 12 nm under Article 3 UNCLOS. As a result, their territorial waters extend only partway toward the middle of the Gulf, preserving a corridor of exclusive economic zones (EEZs). This arrangement allows for freedom of navigation under UNCLOS while maintaining the rights of both countries to monitor and manage activity within their EEZs, particularly in relation to marine environmental protection and exploring and exploiting natural resources under UNCLOS.

The vessels at the centre of the current tensions have been using this corridor to travel to and from Russian ports – often while sailing without a flag and broadcasting false or misleading location information via AIS. Under Article 92(1) UNCLOS and Regulations 19 and 19–1 of Chapter V of the International Convention for the Safety of Life at Sea (SOLAS), a vessel shall sail under the flag of one State, where it shall effectively exercise its jurisdiction and control over the vessel and the ship must broadcast its true location using the AIS at all times during its voyage. Therefore, the behaviour of the shadow fleet is not only deceptive but undermines international maritime law and navigational safety.

These tankers form part of a broader trend. Since the G7 introduced a price cap on Russian oil in December 2022, the use of sub-standard ships has surged. A Resolution adopted by the International Maritime Organization (IMO) defined the shadow fleet not only by its evasion of sanctions, but also by its operational risks: many of these ships have obscured ownership, are poorly maintained, lightly crewed, and prone to incidents. The Baltic Sea is particularly sensitive to these risks. It is home to a high concentration of critical undersea infrastructure, some of which has already suffered damage under suspicious circumstances.

NATO has increased its maritime surveillance in response to this issue; however, the operational enforcement burden has so far fallen to Estonia. Its approach — up to and including boarding and detention of vessels — has raised eyebrows. Yet it also highlights an emerging legal test case: how far can a coastal state go in protecting its maritime domain from vessels that, while technically in compliance with freedom of navigation, clearly undermine good faith maritime conduct?

The Legal Loopholes in the Law of the Sea

UNCLOS gave coastal States very limited power to regulate shipping activities within their jurisdictional waters. Under Articles 58 and 92 the Convention, when a ship is inside the EEZ of any State, it  has the right of the freedom of navigation and is subject to the exclusive jurisdiction of the flag State. This right is extended to the territorial sea of the coastal State in the form of conducting “innocent passages” that are not prejudicial to the peace, good order or security of the coastal State (Article 17). However, these rights only exist in case a vessel is legitimately flying a flag. As noted in Oppenhiem’s International Law, the relationship between flying a flag and possessing the nationality of the flag State is a legal one (p. 287) and only vessels sailing under a State’s flag enjoy freedom of navigation on the open seas. Put differently, the international law of the sea – as enshrined in UNCLOS-grants rights solely to States, not the shipowner or the captain of the vessel. Therefore,  vessels without nationality lack international legal protection and can be subjected to the jurisdiction of all States. In the cases referenced above, KIWALA and JAGUAR were found to be sailing without a flag when it was interdicted by Estonian authorities. Therefore, in both cases, Estonia’s actions complied with the law of the sea.

Alternatively, if a dark ship is flying a flag, even in questionable ship registries that have no interest nor capacity in regulating their fleet, the right of coastal States to interdict such a vessel is very limited. Under Article 110 (Right of visit), a duly authorized vessel of a State can only board a foreign vessel in its EEZ when there “is reasonable ground for suspecting that” the ship (i) is engaged in piracy; or (ii) slave trade; (iii) or unauthorized broadcasting; (iv) is without nationality or (v) has the same nationality as the interdicting State. Apart from these limited circumstances, coastal State enforcement actions without flag State consent would stretch existing frameworks.

Conclusion

The situation in the Gulf of Finland is more than a shipping concern — it is a test of how states apply international law amid deliberate ambiguity. Meanwhile, regional coordination remains uneven. While the EU has updated its sanctions framework to allow inspections of sanctioned vessels passing through member States’ waters if they lack proof of insurance, enforcement remains inconsistent. And while NATO’s surveillance presence is visible, its engagement has so far stopped short of direct intervention. Similar shadow fleet tactics are emerging in Southeast Asia and elsewhere but often go unchallenged. As long as these vessels carry Russian oil above the G7 price cap and outside IMO rules, the threat to maritime safety and regional security will endure. The Baltic Sea may, therefore, be the most visible front, but the challenge is global.