MOSCOW - A RUSSIAN sailor has been formally charged with causing death by negligence after the accident in which 20 people were gassed to death on a nuclear submarine, officials said on Monday.

'The charges were pronounced in terms of article 109' of Russia's penal code, said the chief of the prosecutors' investigating commission Alexander Bastrykin. It provides for up to five years in prison for an individual found guilty of causing death by negligence.

'This is not the only version. We are investigating all the hypotheses. We will consider this very carefully. Everything will be completely objective,' he added, according to the RIA Novosti news agency.

In the accident earlier this month, 20 people died when the Nerpa's fire-extinguishing system was triggered as the submarine was being tested in the Sea of Japan. It pumped Freon gas into the vessel, depriving the victims of oxygen.

The incident was Russia's worst naval disaster since the sinking of the Kursk submarine in the Barents Sea in 2000, in which all 118 sailors on board died. -- AFP