Moscow  - At least 20 sailors and civilians were killed on board a Russian nuclear submarine in an accident apparently caused by a defect in the fire suppression system, a military spokesman said early Sunday.

The accident occurred in a submarine belonging to Russia's Pacific fleet with 208 people on board, Navy spokesman Igor Dygalo said, according to the Interfax agency.

The official said the submarine was not damaged in the accident and no radioactivity was released. There was also no measured rise in radioactivity.

President Dmitri Medvedev was informed about the accident.

At the time of the accident, there were 208 people including 81 sailors on board. The dead included sailors and shipyard workers.

The submarine was on a test cruise, and was heading to port on Russia's Pacific coast.

Eight years ago, all 118 people on board the Russian nuclear submarine Kursk died in an accident after a defective torpedo exploded on board. (dpa)