France says it has seized an oil tanker in the Mediterranean Sea suspected of being part of a "shadow fleet" circumventing Russian sanctions.
French President Emmanuel Macron said the tanker, named Grinch, was "subject to international sanctions and suspected of flying a false flag."
The French navy, with the help of allies including the UK, seized the vessel on Thursday morning between Spain and Morocco. French maritime authorities said a search of the ship "confirmed suspicions regarding the regularity of its flag."
The Russian embassy in Paris said it had not been informed of the seizure.
Moscow's so-called shadow fleet is a clandestine network of tankers used to circumvent Western sanctions on Russian oil exports. It uses older tankers with opaque ownership and insurance arrangements.
French authorities said the Grinch was traveling from the Arctic port of Murmansk in northern Russia when it was intercepted. According to ship tracking websites MarineTraffic and VesselFinder, the vessel was flying the flag of the Comoros.
Announcing the seizure on X, Macron said: "We are determined to uphold international law and effectively enforce sanctions."
He added that the activities of the "shadow fleet" "contribute to financing the war of aggression against Ukraine," and said the vessel had been "diverted."
Defence Secretary John Healey said the UK navy had provided "tracking and surveillance" assistance, with HMS Dagger monitoring the tanker through the Strait of Gibraltar.
He added: "Alongside our allies, we are stepping up our response against shadow vessels to prevent the funds that fuel Putin's illegal invasion of Ukraine." Britain has imposed sanctions on 544 Russian "shadow fleet" vessels.
Ukrainian President Volodymyr Zelensky welcomed the move, saying it was "exactly the kind of resolve needed to ensure that Russian oil no longer finances Russia's war."
"The ships should be seized," he said on X. "And wouldn't it be right to confiscate and sell the oil being carried in these tankers?"
Earlier, speaking in Davos, Zelensky urged Europe to do more to ensure its own security, saying: "Europe likes to discuss the future but avoids taking action."
Many Western countries imposed sanctions on Russian energy after Russia's full-scale invasion of Ukraine in 2022.
In early January, British armed forces supported a US operation in the Atlantic to seize a Russian-flagged tanker that US officials said had violated sanctions by carrying oil for Venezuela and Russia.
Moscow condemned the move, saying no country has the right to use force against properly registered vessels in the jurisdiction of other countries.
Last October, France seized another sanctioned tanker, the Boraq, off its western coast, but released it a few days later.
Shadow fleets are becoming increasingly common, and Venezuela, Iran, and Russia have all been accused of using them to circumvent oil sanctions.
Financial intelligence firm S&P Global estimates that one in five oil tankers worldwide is used to smuggle oil from sanctioned countries.
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