France says it has seized an oil tanker in the Mediterranean suspected of being part of Russia's sanction-busting shadow fleet.

French President Emmanuel Macron stated that the tanker, named the Grinch, was subject to international sanctions and suspected of flying a false flag.

The French navy, in collaboration with allies including the UK, boarded the vessel on Thursday morning between Spain and Morocco. French maritime authorities conducted a search that confirmed suspicions about the illegitimacy of the flag.

Russia's embassy in Paris indicated it had not been informed of the seizure.

Moscow's so-called shadow fleet consists of a clandestine network of tankers evading Western sanctions on Russian oil exports by utilizing aged vessels with obscure ownership and insurance.

The Grinch was reportedly en route from the Arctic port of Murmansk when intercepted, flying a Comoros flag according to ship tracking data.

Announcing the seizure on social media, Macron emphasized the determination to uphold international law and effectively enforce sanctions. He mentioned that the activities of the shadow fleet contribute to financing aggression against Ukraine.

Defence Secretary John Healy noted that the UK navy provided monitoring support, with HMS Dagger tracking the tanker through the Straits of Gibraltar, stating that efforts would be intensified to cut off funding for illegal actions in Ukraine.

Ukrainian President Volodymyr Zelensky praised the seizure, stressing the need for decisive action against such vessels, questioning if it was fair to confiscate and sell the oil onboard.

Many Western countries have imposed sanctions on Russian energy in response to the invasion of Ukraine. Past actions have included the seizure of sanctioned vessels, with France previously taking control of another tanker off its coast.

Fuelled by ongoing global tensions, shadow fleets are reportedly becoming more prevalent, with estimates suggesting one in five oil tankers worldwide may be involved in the smuggling of oil from sanctioned nations.