French forces arrested the captain and first officer of a sanctioned oil tanker suspected of operating in Russia’s “shadow fleet” after boarding the vessel off the Atlantic coast, authorities said Thursday.

The ship, known as Boracay, was intercepted near Saint-Nazaire last weekend by navy commandos. Prosecutors in Brest have launched an investigation on two charges: failing to comply with an order to stop and failing to provide proof of the ship’s flag nationality.

The tanker, also known as Pushpa and Kiwala, is Benin-flagged but subject to EU and UK sanctions. It previously faced detention in Estonia for sailing without a valid registration. 

According to MarineTraffic data, the vessel was approximately 50 nautical miles south of Copenhagen on September 22 when drone activity forced the city’s airport to close.

“Thanks to our Navy commandos and to the crews of the French Navy who intervened this weekend on board a Russian shadow fleet tanker, currently anchored off Saint-Nazaire,” Prime Minister Sebastien Lecornu wrote on X. “Their action contributed to the arrest of two members of its crew.”

Russia is believed to operate several hundred tankers, registered in other countries as part of its shadow fleet, which is used to circumvent international sanctions and continue exporting energy. French President Emmanuel Macron estimated that the fleet numbers between 600 and 1,000 ships.

Kremlin spokesman Dmitry Peskov said Moscow had no information on the tanker but claimed Russia sometimes acts against “provocative actions” from foreign states.

The arrests come as European leaders consider enhancing defense measures in response to recent drone incursions across Europe, including in Romania, Poland and Estonia.