"This morning, the French Navy boarded an oil tanker coming from Russia, subject to international sanctions and suspected of flying a false flag," he said on X in English, adding the operation had been carried out "with the support of several of our allies".

Local maritime authorities said the navy seized an oil tanker called "Grinch" between Spain and Morocco, after it started its journey in the Russian Arctic port of Murmansk.

A ship called "Grinch" is under UK sanctions, while another called "Carl" with the same registration number is sanctioned by the United States and European Union.

Ship tracking websites marinetraffic and vesselfinder said the vessel had been flying a Comoros flag.

"After the team boarded, an examination of documents confirmed the doubts as to the regularity of the flag," the Mediterranean Maritime Prefecture said.

The ship "is currently being escorted by the national navy to a point of anchorage for further verifications," it added.

Images released by the French military showed masked soldiers boarding the Russia-linked ship in an operation involving a navy boat and two navy helicopters.

"We will not tolerate any violation," said Macron.

"The activities of the 'shadow fleet' contribute to financing the war of aggression against Ukraine," he added, referring to the conflict sparked by Russia's 2022 invasion.

Ukraine's President Volodymyr Zelensky was swift to thank Macron.

"This is exactly the kind of resolve needed to ensure that Russian oil no longer finances Russia's war," he responded on X.

"Russian tankers operating near European shores must be stopped. Sanctions against the entire infrastructure of the shadow fleet must be tough," he wrote.

It is the second such boarding in recent months.

France in late September detained a Russian-linked ship called the Boracay, a vessel claiming to be flagged in Benin, in a move Russian President Vladimir Putin condemned as "piracy".

The Boracay's Chinese captain is to stand trial in France in February.

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