The Yekaterinburg Delta-class nuclear submarine caught fire on Thursday during repairs at a shipyard in the northwest Russian Murmansk Region, the local Emergencies Ministry department said.

Fire safety violations during routine maintenance works are seen as the most likely cause of the blaze at a floating repair dock.

No deaths or injuries among the crew and shipyard workers have been reported. However two employees of the Emergency Ministry and seven soldiers were hospitalized with poisoning from the nuclear submarine, a law enforcement source in the Murmansk region said.

“There is no threat of nuclear pollution," it also said in a statement.

Wooden scaffolding around the submarine caught fire, which spread to the submarine's outer hull, Northern Fleet spokesman Capt. 1st Rank Vadim Serga said earlier.

Delta-class submarines have an outer skin of anechoic rubber, designed to absorb sound from sonars to make the boat harder to detect, but which could burn in a dry environment. The boat has a double hull of thick steel, however, which would protect its interior from external fire.

"There is no possibility of fire burning through the hull and no threat to on-board equipment," Serga said.

Military investigators have opened a criminal case into charges of “the destruction or damage of military property due to negligence,” a spokesman from the Investigation Committee said.

The K-84 Yekaterinburg nuclear submarine is one of seven Delta-IV class submarines in service, all deployed in the Northern Fleet. It carries 16 Sineva (NATO classification "Skiff") submarine-launched ballistic missiles.

The Delta-IV class submarines are the core of the naval component of the Russian nuclear triad at present and may remain in service for another 10 years.