France and other countries have vowed to crack down on the sanction-busting shadow fleet of oil tankers which experts estimate numbers over 400 ships.

An oil tanker in the Mediterranean Sea that traveled from Russia, is pictured after being intercepted by France`s Navy on Thursday.Etat-Major des Armees via AP

France`s navy, working with intelligence provided by the United Kingdom, on Thursday intercepted an oil tanker in the Mediterranean Sea that traveled from Russia, in a mission targeting the sanctioned Russian shadow fleet, officials said.

French maritime authorities for the Mediterranean said the ship, the Grinch, is suspected of operating with a false flag. The French navy is escorting the ship to anchorage for more checks, the statement said. The tanker departed from the city of Murmansk in northwestern Russia, it said.

Oil revenue is a key part of Russia`s economy, allowing President Vladimir Putin to pour money into the war effort against Ukraine without worsening inflation for everyday people and avoiding a currency collapse.

France and other countries have vowed to crack down on the sanction-busting shadow fleet of oil tankers which experts estimate numbers over 400 ships. They are also trying to secure deals with flag-carrying countries to make it easier to board the vessels.

Russia is using what is described as a "shadow fleet" to evade sanctions over its war on Ukraine. The fleet is a compilation of aging vessels and tankers owned by nontransparent entities with addresses in non-sanctioning countries, and sailing under flags from such countries.

France`s Navy, working with intelligence provided by the United Kingdom, on Thursday intercepted an oil tanker in the Mediterranean Sea that traveled from Russia.Etat-Major des Armees via AP

"We are determined to uphold international law and to ensure the effective enforcement of sanctions," French President Emmanuel Macron said in a post about the interception, with a photo showing a French helicopter hovering over a ship.

"The activities of the `shadow fleet` contribute to financing the war of aggression against Ukraine," Macron added.

The French mission was conducted together with the U.K, which gathered and shared intelligence that enabled the ship to be intercepted, according to French military officials who spoke to The Associated Press on condition of anonymity to discuss details of the operation.

The ship was operating under a false flag from the Comoros islands, which are off east Africa, and its crew is Indian, the officials said. It was intercepted in the western Mediterranean, off the southern Spanish coastal town of Almeria, the officials said.

Last September, French naval forces boarded another oil tanker off the French Atlantic coast that Macron also linked to the shadow fleet. That tanker traveled from the Russian oil terminal in Primorsk near Saint Petersburg. Known as "Pushpa" or "Boracay" - its name was changed several times - the ship was sailing under the flag of Benin.

Putin denounced that interception as an act of piracy and alleged that Macron initiated the move to deflect attention from French domestic problems.

The tanker`s captain will go on trial in February over the crew`s alleged refusal to cooperate, according to French judicial authorities.