A sailor on board the accident-hit K-152 Nerpa nuclear submarine was found guilty on Thursday by an official probe panel of causing the toxic gas leak that killed 20 people as the Russian military said the vessel was fit for induction into the Russian navy amid reports that it was to be leased to India.

The investigative committee spokesman said the sailor, who was not named, had manually switched on the submarine's fire control system for which he was not authorised and for no apparent reason.

"The sailor has confessed to switching on the vessel's fire extinguishing system for no apparent reason. He was not authorised to do so," the spokesman Vladimir Markin said, contradicting previous claims that the fire control system had gone off on its own or cigarette smoking had triggered it.

The sailor against whom a manslaughter investigation has been opened faces seven years prison term for causing multiple deaths due to his action.

The high-level probe panel set up by President Dmitry Medvedev is expected to submit is final report on Friday.

Despite the accident on board the Akula-II class submarine which occurred on Saturday night during trials in the Sea of Japan [Images], the Nerpa passed its tests and will be authorised for use by the Russian navy, according to the head of the military's general staff, Nikolai Makarov.

"During trials, in spite of the tragic mishap and casualties, this nuclear submarine has demonstrated reliable functioning of its all components and systems," Gen Makarov was quoted as saying by AVN-Interfax . The Russian media had reported earlier that the vessel was to be leased to India on a contract worth 650 million dollars.

According to a spokesperson of the Amur shipyard, the same team will continue sea going trials of the submarine after the probe.

The Saturday night mishap was the second worst naval accident in last 8 years when the Kursk nuclear submarine of the Northern Fleet sank after detonation of its torpedoes killing 118 crew.

There were 17 civilian technical staff of the Komsomolsk-on-Amur based naval shipyard and sub-contractors among the twenty dead and 21 injured, who were checking the submarine for delivery to the Russian Navy.