Forty two sailors died when the Komsomolets sank in 1989

Under a 1995 agreement each side promised to inform the other immediately of incidents like the sinking of the Kursk, but the Russians cancelled the agreement in 1997.

Norway, whose border lies barely 100 km from the Russian city of Murmansk says it is vital to get the system working again.

The governor of Finnmark in northern Norway, next door to Russia, Gunnar Kjonnoy, told BBC News Online that he thought the Kursk was very unlikely to be a problem for the Norwegians.

He said he believed Russian assurances that the submarine's reactors had been shut down, and he expected they would be checking the temperature of the reactors.

He hoped the Russians would salvage the Kursk so there would be no fears of radioactive contamination of the Barent Sea.

Close watch

The Kursk is lying about 300km (184 miles) east of Norway's Arctic coast.

Seawater is checked for radiation

Russia's Atomic Energy Ministry says the radiation risk from the Kursk is minimal because of an automatic protection system designed to shut down the boat's twin reactors in the event of an accident.

But Norway, which already monitors radiation from the Komsomolets, another Russian sub that sank in its waters in 1989, continues to monitor the situation closely.

Norwegian scientists say vigilance is needed since it is not yet clear what caused the boat to sink, or the level of damage it has sustained.

Fears for sub's integrity

Despite Russian experts' claims that the Kursk's reactor will be safe for "many centuries", environmentalists are also demanding that the boat's reactor should be raised as soon as possible.

Nuclear sub losses

1963: USS Thresher sinks off the coast of New England 1968: USS Scorpion lost in the mid-Atlantic 1970: Soviet November class sub sinks 480km north-west of Spain 1986: Soviet sub sinks 960km north-east of Bermuda 1989 : Soviet boat 'Konsomolets' sinks off northern Norway 2000 : Russian Oscar class sub 'Kursk' sinks in the Barents sea

"The Kursk adds another submarine and another reactor to the ocean bed," said a spokesman for the environmental group Greenpeace, William Peden.

"Even if there are no reactor leaks right now, there is the possibility that some time in the future there could be, and this submarine's integrity is already threatened," he added.

Thomas Cochran of the US National Resources and Defence Commission, said: "There's a general feeling to keep ocean pollution as low as reasonably achievable.

"Any amount of radiation causes cancer and... once you start, you don't know where it's going to end up."

Rotting ships

Experts say a wider threat also remains from Russian nuclear vessels lying in various states of disrepair in Russia's northern ports and shipyards.

According to the Bellona foundation, at least half of an estimated 100 laid-up subs still have nuclear fuel on board.

The foundation also believes nuclear waste is being stored in nine rotting ships, and a further 17 nuclear reactors have been dumped in the Kara sea.

A decade ago, the Soviet Navy routinely dumped spent nuclear fuel in Arctic waters, and Russia continued to use far eastern seas for the same purpose until Japan sponsored a proper waste disposal scheme.