The French Navy intercepted a tanker off Saint-Nazaire on suspicion that the vessel belonged to the Russian shadow fleet.

French military personnel boarded the tanker Boracay on Wednesday and detained two of the crew members, news agency France 24 said.

The vessel is now stationed off the coast of western France.

The operation comes as the EU steps up efforts to clamp down on Russia’s shadow fleet. Last month, the bloc added 118 ships to its sanctions list, bringing the total to more than 560 vessels.

The shadow fleet is mainly made up of ageing tankers with opaque ownership structures. The fleet has expanded significantly since Western sanctions on Russia and is widely believed to be used for transporting Russian oil outside of international oversight.