Fourteen sailors have died after a fire broke out on one of Russia's deep-sea submersibles.

The defence ministry said the fire was extinguished due to the "self-sacrifice" of the crew, but did not give any cause of the blaze - or reveal if there were any survivors.

It said the incident happened while the unnamed vessel - intended for studying the seabed - was performing tests.

The underwater craft is now at the Arctic port of Severomorsk, the main base of Russia's Northern Fleet.

Submersibles are usually smaller than submarines - which unlike submersibles can operate over long distances, are autonomous and do not need surface support.


President Vladimir Putin has ordered an inquiry into what happened after cancelling a scheduled event and summoning his defence minister to be briefed on the situation.

Image: Vladimir Putin has ordered an inquiry into what happened

Norwegian authorities said on Tuesday they have not detected abnormally high levels of radiation after the submersible caught fire in the area of the Barents Sea.

Per Strand, a director at the Norwegian Radiation and Nuclear Safety Authority, said Russian officials had told his agency that a gas explosion took place on board.

Russian reports have claimed that it was one of the country's most secret submarines - the nuclear-powered AS-12 Losharik, designed for sensitive missions at great ocean depths - but there was no official confirmation of the claims.

The Losharik, which entered service in 2010, is named after a Soviet-era cartoon character - a toy horse made of small spheres.

The name is said to be explained by the unique design of its internal hull, which is made of several titanium spheres capable of withstanding high pressure at great depths.

Analysts suggested one of its possible missions could be disrupting communication cables on the ocean bed.

The Russian navy also uses Priz-class and Bester-class deep water vehicles, which have a hull built of titanium and are capable of operating at a depth of 1,000m (3,281ft).

Tuesday's fire marks the deadliest Russian naval incident since 2008, when 20 died when a firefighting system was accidentally initiated while the Nerpa nuclear-powered submarine of Russia's Pacific Fleet was undergoing trials.

In the deadliest naval incident in post-Soviet Russia, the Kursk nuclear submarine exploded and sank on 12 August 2000 during naval manoeuvres in the Barents Sea, killing all 118 crew members.