French soldiers have boarded an oil tanker believed to be part of Russia's shadow fleet, used to evade sanctions imposed because of the war in Ukraine.
The Boracay left Russia last month and was off the coast of Denmark when unidentified drones forced the temporary closure of several airports last week. It has been anchored off western France for a few days.
President Emmanuel Macron said the crew had committed serious offences at an EU leaders' summit in Copenhagen on Wednesday but did not elaborate.
Kremlin spokesman Dmitry Peskov said Russia had no knowledge of the vessel.
AFP news agency quoted a source as saying French military personnel had boarded the vessel on Saturday.
Macron refused to be drawn on the question of whether the ship may have been used as a platform for the drone flights that caused such disruption in Denmark last week.
Prosecutors in Brest have opened an investigation on two counts: refusing an order to stop and failing to justify the nationality of the ship's flag.
Many Western countries imposed sanctions on Russian energy by limiting imports and capping the price of its oil following Russia's full-scale invasion of Ukraine in 2022.
To evade these sanctions, Moscow built up what has been referred to as a shadow fleet of tankers whose ownership and movements could be obscured.
France’s President Macron indicated that Russia's shadow fleet could contain between 600 and 1,000 ships.
The Boracay, also known as Pushpa and Kiwala, is a Benin-flagged vessel but has been listed under UK and EU sanctions on Russia. It was detained by Estonian authorities earlier this year for sailing without a valid country flag.
The ship had set off from the Russian port of Primorsk outside Saint Petersburg on 20 September and was scheduled to arrive in Vadinar in north-western India on 20 October. However, it was followed by a French warship after it rounded the Brittany coast and then altered course towards the French coast.
EU leaders have been meeting in Copenhagen under pressure to boost European defense amid recent Russian incursions into EU airspace, including drone interference at multiple Danish airports and military sites.
Danish authorities have yet to find evidence linking Russia to the recent drone disruptions, although they have been part of increasing concerns regarding potential hybrid threats from Russia against European nations.
