Fourteen sailors were killed in a fire on a top-secret Russian submarine, the Russian Defense Ministry said on Tuesday, admitting to one of the country's worst naval disasters in a decade.

A Russian news outlet, RBC, cited an unnamed military source as saying the vessel was a nuclear-powered AS-12 deep-sea submarine known as Losharik, but there was no official confirmation.

The submarine, which is capable of serving under-water cables, was taking carrying out a survey of the sea floor in Russian territorial waters, according to the Defense Ministry. A fire broke out on the vessel, and the sailors died from smoke inhalation. The fire happened on Monday, but was not disclosed until Tuesday.

The submarine has returned to its port, the Northern Fleet Headquarters at Severmorsk, and unconfirmed Russian language reports say some five sailors from the vessel have been hospitalised.

Kremlin spokesperson Dmitry Peskov said on Tuesday that Vladimir Putin, the Russian president, has cancelled a planned public appearance to meet with his defense minister, Sergei Shoigu.

The investigation into what happened on the submarine is being managed personally by Russian navy chief Nikolai Yevmenov.

Monday's fire was compared to fate of the Russian nuclear-powered submarine Kursk.

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