French President Emmanuel Macron on Monday posted a video on X showing commandos rappelling from helicopters onto the Tagor, during an operation that occurred the previous day in international waters 740 km west of Brittany.
The tanker, which had sailed from Russia's Arctic port of Murmansk, was suspected of flying under a false flag, and was intercepted with support from Britain, Macron said. According to the vessel tracker MarineTraffic, the 252-metre-long tanker was sailing under the flag of Madagascar.
France's Maritime prefecture, the state authority for maritime security, said the boarding team's inspection of the vessel's papers had "confirmed suspicions regarding the irregularity of the flag flown."
To try to skirt Western sanctions, Russia has relied on old vessels, known as the shadow fleet, to ship its oil and gas. France and Britain have both vowed to obstruct such vessels as part of a European strategy to combat the oil revenues that help fund Russia's war efforts in Ukraine.
"It is unacceptable for ships to circumvent international sanctions, violate the law of the sea, and finance the war that Russia has been waging against Ukraine for more than four years," Macron wrote on X.
On Monday, the Tagor was steaming under naval escort towards an anchorage off northwestern France, according to the Maritime prefecture.
The Tagor is the fourth sanctioned tanker the French have intercepted.
The EU has imposed 19 packages of sanctions against Russia, but Moscow has adapted to most measures and continues to sell millions of barrels of oil to countries such as India and China, typically at discounted prices.
Western sanctions and a small number of interceptions have had little obvious impact on the 'shadow fleet' at a time oil prices pushed higher by the Iran war offer tankers a big incentive.
Instead it is the Ukrainian strikes on Russian oil facilities that are stopping Moscow from capitalising on the spike in global fuel prices.
Moscow's reaction to the seizure will be closely watched. Kremlin spokesman Dmitry Peskov told journalists on Monday Russia would take measures to ensure the safety of shipping cargo in response to the incident.
In April, Russia deployed a frigate to escort two sanctioned vessels through the English Channel and the Kremlin said Russia had the right to defend itself against what it called piracy.
Days later Estonia said it would refrain from detaining Russian shadow fleet tankers, worried that such actions could provoke a military response from Moscow.
British Prime Minister Keir Starmer said in March he had granted permission for the UK military to board ships belonging to the 'shadow fleet'.
However, shipping data shows dozens of sanctioned vessels have continued to cross UK waters.
