A fire broke out on one of the Russian navy's deep-sea research submersibles and toxic fumes from the blaze killed 14 sailors aboard, Russia's Defence Ministry said Tuesday, although it released few details about the disaster or the vessel involved.

The Defence Ministry did not say how many sailors were aboard the vessel during Monday's fire, whether there were any survivors, or if it was submerged at the time. But Russian media reported it was Russia's most secret submarine, a nuclear-powered vessel designed for sensitive missions at great ocean depths.

Russian President Vladimir Putin, who came under criticism for his handling of the Kursk nuclear submarine disaster in 2000 that killed 118 sailors, cancelled a scheduled appearance and immediately summoned Defence Minister Sergei Shoigu for a briefing on the blaze, which was under investigation.

"Fourteen submariners have died of poisoning by fumes from the fire," Shoigu told Putin during their televised meeting.

"The fire was extinguished thanks to the crew's resolute action."

Putin ordered Shoigu to fly to the Arctic port of Severomorsk, the main base for Russia's Northern Fleet where the vessel was brought, to oversee the investigation and report back to him personally.

Putin, left, and Defence Minister Sergei Shoigu meet in Moscow on Tuesday to discuss a recent accident on board a Russian deep-sea submersible, which caught fire Monday in the area of the Barents Sea. (Sputnik/Alexey Druzhinin/Kremlin/Reuters)

"It's a huge loss for the navy," Putin said. "I offer my sincere condolences to the families of the victims."

He added that the vessel had a special mission and an elite crew.

"It isn't a regular vessel. It's a research vessel with a highly professional crew," Putin said, adding that seven of the dead had the rank of captain and two were awarded the nation's highest medal, the Hero of Russia.

The fire broke out while the submersible was measuring sea depths in Russia's territorial waters, the Defence Ministry said, adding that that the vessel is also used for studying the seabed.

Advanced and obscure

Russia's RBC online news outlet reported that the vessel was the nuclear-powered AS-12 Losharik.

The Losharik, which is believed to have entered service in 2010, is the most advanced and most obscure Russian submarine. It's named after a Soviet-era cartoon character, a toy horse made of small spheres.

The name apparently derives from the unique design of its internal hull, which is made of several titanium spheres capable of withstanding high pressure at great depths.

In 2012, the Losharik was involved in research intended to prove Russia's claim on the vast Arctic seabed. It collected samples from the depth of 2,500 metres, according to official statements at the time. Regular submarines can typically dive to depths of up to about 600 metres.

This 2005 picture shows a Russian Priz-class deep-water vehicle, one of the classes used by the Russian navy. (Jonathan Holloway/AFP/Getty Images)

Some observers speculated the Losharik was capable of going as deep as 6,000 metres, but the claims couldn't be independently confirmed. Analysts suggested one of its possible missions could be disrupting communication cables on the ocean bed.

The Losharik is carried under the hull of a mother submarine, the nuclear-powered Orenburg.

Russian news reports said while the Losharik officially belongs to the Northern Fleet, it answers directly to the Defence Ministry's Department for Deep-Sea Research, reflecting the high sensitivity of its missions.

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 1,000 metres. They are transported to the area of operation by a carrier vessel and can operate autonomously for up to 120 hours.

The blaze marks the deadliest Russian naval incident since 2008, when 20 died after a firefighting system was accidentally initiated as a 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 Aug. 12, 2000, during naval manoeuvres in the Barents Sea, killing all 118 crew members.