Freon released by the unsanctioned use of a fire extinguishing system killed 20 people aboard a Russian submarine, officials said Sunday.

The gas suffocated the victims aboard the nuclear sub, which included 14 civilians and six sailors. Twenty-two more people injured. The vessel was undergoing sea trials in the Pacific Ocean at the time, investigators told RIA Novosti.

The name of the submarine was not released, but officials told the Russian news agency it was an Akula II class Nerpa nuclear attack submarine that was part of Russia's Pacific Fleet. Capt. 1st Rank Igor Dygalo, an aide to the Russian Navy commander, said 208 people, including 81 service personnel, were on board the sub when the incident happened.

Dygalo said the sub's reactor wasn't affected and radiation levels were normal, something that was confirmed to RIA Novosti by an unnamed source in the Pacific Fleet who said the damage had been confined to sub's nose section.

Officials described the incident as Russia's worst submarine accident since the sinking of the Kursk in 2000, which killed 118 sailors.