Russian news agencies say a nuclear submarine that was under repair in a far northern port has caught fire.

The reports of the fire by the state-run Tass and RIA Novosti cited only unnamed sources and Navy officials could not immediately be reached for comment on Tuesday.

Tass cited a source as saying the critical elements of the submarine's reactor had been removed before repair work began.

The submarine is under repair in a shipyard in Severodvinsk, about 620 miles north of Moscow on the White Sea, the reports said.