Fourteen Russian sailors on board a deep water research sub were killed in a fire while carrying out a survey of the sea floor, the Russian defence ministry was quoted as saying by Russian news agencies.

A Russian news outlet, RBC, cited an unnamed military source as saying the vessel was a nuclear-powered

AS-12 deep sea submarine, but there was no official confirmation of that.

The incident took place on Monday in Russian territorial waters and the fire has been extinguished. The vessel is now at the Russian Northern Fleet’s base in Severomorsk on the Barents Sea, and an investigation has been launched to establish the cause, agencies Interfax, RIA and Tass quoted the ministry as saying.

“Fire broke out on board a deep-water scientific research vessel that was studying the marine environment of the world ocean on behalf of the Russian navy,” Interfax cited a ministry statement as saying. “Fourteen submariners died as the result of smoke inhalation.”

The statement as cited by the agencies did not identify the type or model of the vessel.

In August 2000, the Russian nuclear-powered submarine Kursk sank to the floor of Barents Sea after two explosions in its bow, killing all 118 men aboard.

That accident, soon after President Vladimir Putin took office, focused official attention on the state of the military and its hardware.

Since then, Putin has overseen a massive increase in military funding that has allowed the armed forces to renew their equipment and improve training and morale.

However, accidents have continued to happen as the military, used by the Kremlin to project its growing international muscle, has ramped up its activities and extended into new theatres of operation.

In December 2016, a Russian military plane carrying 92 people, including dozens of Red Army Choir singers, crashed into the Black Sea en route to Syria where Russian forces are deployed. Everyone on board was killed.

Russia’s military has been developing new submarines as part of a broader push for new defence hardware under Putin that has also included hypersonic missiles. US media have cited Pentagon officials as saying they are concerned about the activities of Russian submarines and spy ships operating in the ocean off the US coastline.