The Kremlin on Wednesday said details of a fire that killed 14 crew on a deep-water submersible will not be made public because they include classified information.
"This information cannot be made public completely," Kremlin spokesman Dmitry Peskov said. "It belongs to the category of state secrets."
The seamen died on Monday in Russia's territorial waters in the country's far-north, but the disaster was only made public Tuesday.
Peskov said however that President Vladimir Putin was informed right away.
"It is completely normal when this kind of information is not made public," Peskov said, adding that this was "within the law of the Russian Federation".
Officials have given little information about the vessel or the circumstances of the accident, with local media reporting the ship was a secretive nuclear-powered mini-submarine.
The presence of many senior ranking officers on board could suggest the submarine was not on an ordinary assignment.
Peskov said that "no decision has been made" about a period of mourning in the northern Russian region.
The defence ministry said the 14 crew were killed by inhaling poisonous fumes after a fire broke out on a "scientific research deep-sea submersible" studying the sea floor.
However the Novaya Gazeta newspaper cited sources as saying that the accident took place on an AS-12 nuclear mini-submarine, which is capable of going to extreme depths.
