Coast Guard Cutter Munro monitors oil tanker Bella 1 in North Atlantic Ocean, 6 January 2026. U.S. Coast Guard photo / DVIDS

In January, US enforcement authorities engaged in a weeks-long pursuit of an aging, rusty oil tanker heading north away from Venezuela through the Atlantic Ocean. Mid-pursuit, the tanker’s crew did something unexpected: they hurriedly painted a Russian flag on the hull. US forces, supported by the UK military, went ahead and seized the ship anyway, despite Russia having added the tanker to its Maritime Register of Shipping and formally asking the US to halt its pursuit as well as dispatching a naval vessel in response.

The seizure of the oil tanker demonstrates a major shift in global sanctions enforcement. It’s part of a growing trend whereby the so-called shadow fleet - used to bypass Western sanctions restrictions and transport oil from Venezuela, Iran or Russia to buyers around the world – is choosing to ‘emerge from the shadows’ and seek Russian protection to evade capture. According to Lloyd’s List, over 40 shadow fleet vessels have taken on the Russian flag since June, with 17 joining the Russian shipping register in December. ‘There is no question that this trend is a risky one, as it could lead to escalation, and to be frank that might be the Kremlin’s ultimate strategy,’ says Federica D’Alessandra, Co-Chair of the IBA’s Rule of Law Forum.

Gonzalo Saiz Erausquin, a research fellow at British defence and security think tank RUSI, says that the US seizure of the Russian-flagged tanker highlights a clear tension between the US, which wants to aggressively enforce its blockade of sanctioned oil tankers entering and leaving Venezuela, and Russia, which wants to prevent the growing interception of shadow fleet vessels. ‘Russia was willing to come out of the shadows,’ says Saiz Erausquin, ‘abandoning the opaque operations that had been running to date and ultimately assuming quite significant risks around its position as a flag state with regards to the liability that stems from it.’

Saiz Erausquin says that the sudden registering of the tanker under a Russian flag during a pursuit is highly questionable under international law and ‘is a dire statement on the landscape of flag registry globally, where Russia is increasingly admitting it is not upholding international standards and providing registration to a fleet that should no longer be at sea’.

D’Alessandra, who is also Deputy Director of the Oxford Programme on International Peace and Security, says that even if tankers flying the Russian flag do not prevent enforcement efforts the aim is to create a pretense to claim that the pursuing force committed an unlawful act or an act of aggression. ‘That’s typical Kremlin strategy: create confusion, hedge your bets, and lay the ground for false flag operations aimed at shifting the blame on anyone other than themselves,’ she says.

In addition to the US, enforcement authorities in Europe have stepped up efforts to seize shadow fleet tankers in response to concern about their widespread use to circumvent sanctions on Russian oil exports introduced following Russia’s invasion of Ukraine in 2022. Two weeks after the US seizure, the French Navy intercepted a tanker in the Mediterranean Sea, which was released after its owner paid a multimillion pound fine. In December, Finnish police detained an oil tanker suspected of sabotaging an undersea cable between Finland and Estonia.

The UK assistance to the US seizure in the Atlantic Ocean is the first time the UK has been involved in the interception of a shadow fleet tanker. The UK government said it provided ‘operational support […] in full compliance with international law,’ including RAF surveillance. Saiz Erausquin says it’s likely the UK hasn’t carried out its own seizures so far due to the risks of retaliation from Russia. It also involves high costs - associated with maintaining the detained vessels - and complex legal questions. ‘For an actor that wants to abide by international law, hindering the rite of passage and freedom of navigation is something that creates a lot of uncertainty in the UK,’ he says.

Other steps taken by Western allies to combat the shadow fleet include targeted sanctions on individual ships and increased international cooperation to disrupt their movements. Anders Amstrup Fournais, a partner at Hafnia Law Firm in Copenhagen, says that the EU should use existing environmental legislation and laws under the UN Convention on the Law of the Sea (such as the requirement of a ship to carry valid insurance) to intercept shadow fleet tankers. This would, though, require the EU to resolve the issue of these rules potentially conflicting with sanctions restrictions. ‘There is a conflict between the sanctions and environmental laws because if there is a catastrophic oil spill in Danish waters and the insurance provider for the ship is Russian, you’ll never get the money from them,’ he says. Fournais adds that, unless there is substantial evidence of a crime, the ability of EU states to seize ships is extremely limited.

Saiz Erausquin believes the international community should leverage the Financial Action Task Force - which has the mandate to assess countries on their implementation of UN security council resolutions - to place greater value on the oversight of flag registries to deter countries from allowing tankers to use flags of convenience. ‘If we were to include flag registries more comprehensively into effective FATF assessments’ he says, ‘this could lead to greater change in those jurisdictions that want to receive a positive rating in order to access the international financial system.’

Robert Denig, partner at Holland & Knight in New York and officer of the IBA’s Maritime and Transport Law Committee, says he expects the US’ sanctions enforcer, Office of Foreign Assets Control (OFAC), to continue to focus on investigating commercial transactions and intermediaries to target enablers of the shadow fleet. This can be a very difficult task for enforcement agencies with details of ownership and management of the vessels made deliberately opaque.