At least 20 people have died in an incident involving the failure of a fire extinguishing system on a Russian nuclear submarine, local media report.

Russian Pacific Fleet spokesman Igor Dygalo said both sailors and shipyard workers died in the incident, which occurred during sea trials.

He said the submarine itself had not been damaged and there had been no radiation leaks.

Military prosecutors are investigating the incident.

Injured evacuated

The submarine, whose name and class have not been revealed, has been ordered to suspend sea trials and return to port in the far eastern Primorskiy territory, Capt Dygalo said.

"I declare with full responsibility 

that the reactor compartment on the nuclear-powered submarine is working normally and the radiation background is normal," he said, quoted by Itar-Tass news agency.

There were 208 people on board at the time, 81 of whom were servicemen.

Twenty-one injured people have been evacuated from the submarine, sources at the fleet said.

They have been taken to Vladivostok on the destroyer Admiral Tributs.

Reports say the incident occurred in the nose of the submarine. The nuclear reactor, which is in the stern, was not affected.

A shipyard source told the RIA Novosti news agency the vessel was the K-152 Nerpa, an Akula-class submarine, but this cannot be

independently confirmed.

RIA said the trials were in the Japanese Sea and that the Nerpa was due to be leased to the Indian navy.

The agency quoted a Pacific Fleet source as saying the submarine would arrive back at its port at around 0900 GMT on Sunday, depending on weather conditions.

Russian President Dmitry Medvedev is being kept fully informed about the incident, his press service said.

Deputy Defence Minister Alexander Kolmakov and Navy Commander-in-Chief Vladimir Vysotsky are flying to the scene of the incident.

Russia's worst submarine disaster happened in August 2000, when the nuclear-powered Kursk sank in the Barents Sea. All 118 people on board died.