Officials said efforts to partially sink the submarine at the dock had failed to fully extinguish the fire [Reuters]

A huge fire has engulfed a Russian nuclear submarine as it was being repaired, sending flames and smoke billowing into the sky, but officials said all weapons had been removed and there was no radiation risk.

More than 100 firefighters launched a massive operation on Thursday to douse the flames after the blaze broke out on the 11,740-tonne Yekaterinburg while it was docked in the northern Murmansk region near Russia's border with Norway.

Television pictures showed a giant plume of smoke above the yard as firemen struggled to douse flames which witnesses said rose 10 metres above the stricken vessel.

Emergency workers said efforts to partially sink the submarine at the dock had failed to fully extinguish the fire.

The fire was eventually put out about five hours after it first started in the Roslyakovo dockyard near one of Russia's main naval bases, Igor Konashenkov, defence ministry spokesman, said, quoted by the Ria Novosti news agency.

"In order to prevent a new fire breaking out, the submarine will be lowered into the water before returning to its original position," he added.

Nuclear missiles removed

The vessel had all its nuclear missiles and conventional rockets removed before entering the dock, Konashenkov had told state television earlier.

Thursday's fire occurred near the closed town of Severomorsk, one of the Russian navy's main bases.

It is not yet known how the fire started, but a spokesman for the Russian military prosecutor, quoted by Ria Novosti, said a criminal probe had been launched into the "reckless destruction or damage of military assets".

The fire broke out on wooden scaffolding surrounding the submarine and spread to its outer hull, Northern Fleet navy spokesman Vadim Serga told the Interfax news agency.

The Delta IV class vessel was commissioned by the former Soviet Union in 1985 and can carry up to 16 inter-continental ballistic missiles, according to Russian press descriptions of the submarine.

Russia is believed to have six Delta IV submarines, which form the backbone of its sea-based nuclear defences.

The worst disaster to befall the Northern Fleet in recent years was the sinking of the Kursk nuclear submarine in August 2000, which killed all 118 seamen aboard when it caught fire and exploded in the Barents Sea.

Source: Agencies