Russia says one of its nuclear submarines has been damaged by a surge in air pressure, downplaying earlier reports of an explosion.
A ballast tank aboard the submarine was damaged in what a navy official described as a minor incident, according to the Interfax news agency.
No casualties were reported and radiation levels at the White Sea port of Severodvinsk are said to be normal.
The incident took place as the submarine was being repaired.
According to the Reuters news agency, the Russian navy usually shuts down reactors and removes nuclear fuel during repairs to its submarines.
"The management of the [dockyard]... considers the accident as minor," Russian navy spokesman Igor Dygalo told the Itar-Tass news agency.
An environmental official in Norway, near the port of Severodvinsk, told Reuters there was no sign of increased radioactivity as a result of the accident.
Russia's Ekho Moskvy radio earlier reported that an explosion had damaged more than 20sq m (215sq ft) of the submarine's hull.
Russia's ageing fleet of nuclear submarines has a history of deadly accidents.
The worst case in Russia's recent history was the destruction of the Kursk submarine in 2000. It sank to the floor of the Barents Sea after two explosions on board, killing all 188 crew.