Officials say firefighters have finally put out a blaze aboard a nuclear submarine docked in northern Russia, and that there has been no radiation leak.

Authorities said Friday an undisclosed number of crew members monitoring temperatures and carbon dioxide levels inside the Yekaterinburg nuclear submarine were not in danger.

At least seven people, including firefighters, were taken to the hospital for smoke inhalation after the fire erupted Thursday.

The blaze began while the vessel was docked for repairs in the northern Murmansk region.

Russia's military says the blaze started on wooden scaffolding and then engulfed the sub's outer hull.

The military said all of the submarine's weapons had been unloaded before the repairs and its reactor had already been shut down. The Delta IV class vessel is able to carry 16 intercontinental ballistic missiles.

Video footage showed large clouds of smoke rising from the area. The blaze is believed to have started on the wooden scaffolding at the shipyard.

The Kremlin said President Dmitry Medvedev has ordered an investigation into the incident and demanded punishment for anyone found responsible.

In August 2000, Russia's Kursk nuclear submarine sank at sea, killing all 118 crew members on board.