French officials have taken the Indian captain of a suspected Russian shadow fleet tanker into custody days after the oil tanker was seized.

On Thursday, the French navy intercepted the tanker - named the Grinch - which President Emmanuel Macron said was "subject to international sanctions and suspected of flying a false flag".

The Grinch had been travelling through the Mediterranean Sea from the Russian Arctic port of Murmansk. It is now moored, under guard, at a southern French port near Marseille.

Although Moscow is yet to comment, Macron said on Thursday that the shadow fleet helped to "finance Russia's war of aggression against Ukraine".

The office of the Marseille prosecutor office said the rest of the ship's crew members - all also Indians - were being "kept on board" while the 58-year-old captain was taken into custody.