UPDATED Russian navy blames crew member for the deadly accident on Nerpa submarine

Prosecutors said that the unnamed submariner had switched on the Nerpa's fire extinguishing system "without permission or any particular grounds". Twenty died and 21 were injured after they inhaled freon gas released inside the vessel by the safety system.

The man had already been charged and faced up to five years in prison.

The statement contradicted earlier assertions by investigators that the firefighting system on board the attack submarine had triggered automatically and that there was no evidence of human interference. They later ruled out any malfunction.

Critics of the investigation suggested that the sailor was being made a scapegoat.

nterfax news quoted an unnamed officer from the Nerpa's crew who expressed scepticism over the man's guilt. He said: "We have served together for a long time - since 2003. He is not green. He is a skilled specialist and it is not the first year that he is serving in the navy.

"We don't believe that he is guilty and fear that he could have confessed under pressure. He was taken away for interrogation yesterday and has still not come back."

Survivors of the disaster told a Russian newspaper that gas masks issued to crew members had been faulty. Warrant officer Yevgeny Ovsyannikov told Tvoi Den: "I saw people in convulsions ripping off their masks. I also had a breathing apparatus on, but it only worked for seven to 15 minutes."

Dmitri Usachyov, another man on board, said: "Some of the dead were found with their gas masks on. The breathing apparatuses simply didn't work."

The accident was the worst for Russia's Navy since the explosion that sank the Kursk nuclear submarine and led to the deaths of all 118 crew in August 2000.