The Kremlin on Wednesday refused to reveal the full story of a fire that killed 14 officers on what was reportedly a nuclear-powered mini-submarine, saying the details of the tragedy were a "state secret."

But apparently under pressure from critics, the defence ministry published the names and photographs of the victims who it said had saved "their comrades and the deep-sea submersible" at the cost of their lives.

Defense Minister Sergei Shoigu said there were survivors of the accident, without specifying numbers.

The seamen died on Monday due to smoke inhalation, the defense ministry said, following the fire on a submersible in the Barents Sea in Russia's territorial waters, but the accident was only made public on Tuesday.

Two days after the tragedy the defense ministry described the victims as "true patriots" and top professionals, adding they repeatedly took part in expeditions to study the Arctic and plunged to "maximum depths."

Russia has been involved in the battle for the Arctic, staking a claim for the Arctic Ocean and its riches.

The tragedy has echoes of the sinking of the Kursk submarine in 2000, also in the Barents Sea, that claimed 118 lives and shook the first year of Vladimir Putin's presidency.

Officials have released little information, saying the crew was studying the sea floor in the interests of the navy. But Russian media reported the ship was a top-secret nuclear-powered mini-submarine.

Putin's spokesman Dmitry Peskov explained the secrecy surrounding the tragedy by saying the information was a "state secret."

Putin did not go to a military base in the northern city of Severomorsk where the vessel is now, dispatching Shoigu instead.

The Kremlin also did not declare a nationwide day of mourning.

- 'Complicated task' -

Igor Kurdin, a former commander of a nuclear submarine, said authorities have managed to extract only four bodies from the vessel which was full of water.

"It's a complicated task," Kurdin told Echo of Moscow radio. "When and most importantly in what state the rest of the bodies will be taken out is unclear so far."

Independent newspaper Novaya Gazeta said the accident took place on an AS-12 nuclear mini-submarine.

Little is known about it and no official photographs of the vessel are available.

Conceived in the Soviet era and launched in 2003, the AS-12 is apparently carried by a "mother" submarine and is designated for research and special military operations.

Its hull is reportedly built of titanium orbs, earning it the nickname "Losharik" --- a winsome toy horse made of juggling balls in a Soviet-era cartoon.

The acting governor of Saint Petersburg said the crew was based in the city.

The presence of many senior ranking officers on board could suggest the submarine was not on an ordinary assignment, experts said.

They described the crew as an elite unit of highly-skilled hydronauts. Putin has described the tragedy as a "big loss" for the army.

Nearly all of the victims were highly decorated officers and included seven Captain First Rank officers -- the most senior staff officers in the Russian navy.

Two have been awarded Hero of Russia, a top title given out by the president.

Shoigu -- who was on Wednesday in Severomorsk, the restricted-access Arctic port -- said that after evacuating a civilian, the crew closed the hatch to halt the spreading of flames.

"They fought for the ship to survive until the end," he said, adding that the seamen would be posthumously given state awards.

- Echoes of Kursk disaster -

Churches in the Arctic city of Murmansk and in Kronstadt, a naval base in the Gulf of Finland, will hold services in their memory.

The navy was considering burying the victims in Saint Petersburg's historic Serafimovskoye cemetery, near the graves of those who died in the Kursk submarine.

In August 2000, the Kursk submarine sank in the Barents Sea with the loss of all 118 aboard.

Putin was severely criticised for his response.

A military expert, who spoke to AFP on condition of anonymity, rubbished claims Monday's fire happened during scientific research.

"Usually it's a cover for different type of work conducted on the seabed" like laying or tapping cables, he said.