Green activists have expressed concern that the vessel will be sailing past several European countries on its way home during the winter storm season.

The Sevmorput vessel had to turn around on December 2 and is travelling towards the Russian port city of Saint Petersburg at a speed of 10 knots, Rosatom said.

The vessel was forced to stop off the coast of Angola for "repairs of the propeller and rudder system", Rosatom told AFP, explaining that the propeller lost one of its blades.

During maintainance work that lasted three weeks due to unfavourable weather conditions, another propeller blade was cut off to remove the imbalance, the nuclear agency added.

Rosatom added that the ship was seaworthy and its nuclear reactor was operating without any complications.

But the French environmental group Robin Hood expressed concern Monday about Sevmorput's route, noting that it would pass 14 European countries on its way to Saint Petersburg.

Sevmorput's journey past Europe will be taking place during "winter storms in the North Atlantic", the organisation said in a statement.

There was "no coordinated plan between EU countries to prevent the floating nuclear power plant from drifting" or over arranging another port for the vessel to dock, it added.

According to the Marine Traffic tracking website, Sevmorput is currently in the Atlantic Ocean between the Canary Islands and the Moroccan coast. It estimated it would take several weeks to get back home.

Sevmorput is Russia's only active nuclear-powered cargo ship, a 260-metre-long vessel commissioned during the Soviet era and completed in 1988.

It returned to service in 2016 after extensive repairs.