MOSCOW - At least 20 people died and 21 were injured in an accident on board a Russian nuclear-powered submarine in the Pacific Ocean, a Russian naval spokesman said on Sunday.

Radiation levels on board were normal, he said.

Russia’s navy has suffered a string of fatal accidents, including the loss of the Kursk nuclear submarine in the Barents Sea in August 2000. All 118 sailors aboard died.

“More than 20 people were killed on a nuclear submarine in the Pacific Ocean during routine testing as a result of the unsanctioned functioning of the fire extinguishing systems,” the navy spokesman, Igor Dygalo, said by telephone.

Dygalo did not give the name of the submarine or specify where it was located. There were 208 people on board at the time of Saturday’s accident, some of them from a shipbuilding company, he added.

“The reactor section (of the submarine) is working properly,” the spokesman said. “The radiation levels on the ship are normal.”

A Russian destroyer, the Admiral Tributs, was providing assistance and taking some of the injured crew from the submarine to port, Dygalo said.

He did not say where the ships were but the Tributs is normally based at Vladivostok, Russia’s main Far Eastern naval port, according to Russian media.

President Dmitry Medvedev has been informed about the accident, Russian news agencies reported.

The state-owned RIA news agency quoted a highly placed official in the Pacific Fleet as saying the accident happened in the bow of the submarine.

In August 2005, seven Russian sailors were freed with help from a British rescue crew after three days trapped inside an AS-28 mini-submarine 600 feet down in the Pacific with dwindling air supplies.