The accident, which happened while the submarine was on sea trials in the Pacific Ocean, was the deadliest to hit Russia's navy since the Kursk nuclear submarine exploded beneath the Barents Sea in 2000, killing all 118 sailors on board.

The Kremlin is seeking to establish itself as a global power and is using the military to project its influence. A flotilla of warships is heading to U.S. foe Venezuela for the biggest maneuvers in the Caribbean Sea since the Cold War ended.

"This most recent incident signals that, though Russia is increasingly assertive and aggressive on the geopolitical stage, it still faces very real challenges in terms of the revitalization of its naval power," Stratfor, a U.S.-based consultancy, said in a commentary.

VLADIVOSTOK, Russia (Reuters) - Twenty people were killed on board a Russian nuclear submarine, the navy said on Sunday, in an accident that exposed the gap between the Kremlin's ambitions and its military capability.