At least 20 people have died in an accident on a Russian nuclear submarine when a fire extinguishing system was activated by mistake.
Russian Pacific Fleet spokesman Igor Dygalo said both sailors and shipyard workers died in the accident, which occurred during sea trials.
The dead were suffocated by freon gas, which is used to put out fires as it removes oxygen from the air.
The vessel was not damaged and there was no radiation leak, Mr Dygalo said.
It is the worst incident for the navy since the sinking of the Kursk submarine in 2000, which left 118 dead.
Military prosecutors are investigating the incident, but the name and class of the submarine involved have not been officially revealed.
There were 208 people on board at the time, 81 of whom were servicemen. The dead are reported to be six sailors and 14 civilians.
Twenty-one injured people, reported to be suffering from various degrees of poisoning, were transferred from the submarine to the destroyer Admiral Tributs and taken to hospitals near Vladivostok.
1. Personnel working in front section of submarine affected when fire extinguishers set off unexpectedly
2. Affected area may have been sealed off, trapping personnel inside. There were more staff than usual on board as submarine was undergoing tests
3. Fire extinguishers release freon gas, which displaces breathable oxygen, causing workers to suffocate
4. Twenty people die and 21 are injured
The dead were transferred to morgues nearby after the vessel, which had been undergoing sea trials in the Sea of Japan, returned to port at Bolshoi Kamen, near Vladivostok, in the far eastern Primorsky territory.
Capt Dygalo said the incident happened after the fire extinguishing system "went off unsanctioned".
But questions are being asked about why there were so many casualties.
Vera Sanzhonova, the wife of one of those on board, said she had not had word about her husband since the accident.
"My husband is not in the list of injured, and not in the list of dead. Many have already called their wives and said that they are okay, but he hasn't called me. I know that some people have not been identified yet," she said.
The BBC's Richard Galpin in Moscow says that in normal cases of a fire on board a submarine, the area would be evacuated and sealed off before pumping in freon gas.
RUSSIAN SUBMARINE DISASTERS
6 Sept 2006: Two die after fire in Viktor-III class Daniil Moskovsky
28 Aug 2003: Nine die after decommissioned November class K-159 sinks
12 Aug 2000: 118 die in sinking of Oscar-II class Kursk
7 Apr 1989: 42 die after fire in Soviet-era Komsomolets
The gas removes oxygen from the air - to put out the fire - but if anyone is still trapped inside that area, they face suffocation.
Vladimir Markin, an official from Russia's top investigative agency, later said forensic tests had confirmed that freon was the cause of death.
Reports say the incident occurred in the nose of the submarine. The nuclear reactor, which is in the stern, was not affected.
"I declare with full responsibility that the reactor compartment on the nuclear-powered submarine is working normally and the radiation background is normal," Capt Dygalo said, quoted by Itar-Tass news agency.
A shipyard source told the RIA Novosti news agency the vessel was the K-152 Nerpa, an Akula-class submarine, but this has not been confirmed.
Russian Pacific Fleet spokesman Igor Dygalo said there had been no radiation leaks
The Nerpa is due to be leased to the Indian navy, and Indian naval personnel were due to travel to Vladivostok earlier this month to train on board the submarine ahead of its transfer, according to the website Indian Defence.
Russian President Dmitry Medvedev is being kept fully informed about the incident, his press service said.
Deputy Defence Minister Alexander Kolmakov and Navy Commander-in-Chief Vladimir Vysotsky are flying to the scene of the incident.
Russia's worst submarine disaster happened in August 2000, when the nuclear-powered Kursk sank in the Barents Sea. All 118 people on board died.
The then president, Vladimir Putin, was criticised for being slow to react to the incident and reluctant to call in foreign assistance.
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