French authorities have taken into custody the Russian captain of a seized oil tanker believed to be part of Moscow's "shadow fleet," a prosecutor said Wednesday.

The French Navy detained the Tagor on Sunday in international waters with British help after the vessel allegedly failed to comply with orders and was suspected of sailing under a false flag.

It is the fourth ship that France has seized since September on suspicion of belonging to the "shadow fleet," a network of aging tankers that Western governments say has helped maintain Russian oil exports despite sanctions imposed after Moscow's 2022 invasion of Ukraine.

The tanker arrived in a harbor in Brittany on Tuesday.

The captain faces up to one year in prison and a fine of 150,000 euros ($174,000), Brest prosecutor Stéphane Kellenberger said.