Soviet nuclear submarine 500 miles east of Bermuda.

It was previously thought three people died aboard the K-219 sub when it sank.

Now it has emerged a fourth sailor, Sergei Preminin, died after becoming trapped in the sinking sub.

He had been lowering by hand the containment bars of one of the vessel's two reactors.

The sub, which sank in 18,000 feet of water, was carrying 15 strategic nuclear missiles, and had 113 sailors on board.

The accident was dubbed by the environmental group Greenpeace a "maritime Chernobyl''.

It predicted 100 people would eventually die from the sub's radioactive agents swept by ocean currents around the globe.

And yesterday a local Greenpeace spokesman raised renewed fears over the impact of the sinking.

Experts, however, say it would take years for radioactive waste to get to the surface and it would be widely diluted by ocean water.

But Soviet officials released no details at the time, save to say the vessel sank following a fire and posed no environmental danger.

Last week the Russian newspaper Trud, citing secret military documents, reported the Soviet military had probed the incident.

It reported an explosion in one of the vessel's missile shafts caused a fire, and released toxic gases.

Sailors inside the compartment inhaled the yellowish fumes, and three died, Trud claimed.

It added an emergency system was activated and shut down one of the submarine's two reactors.

When Moscow ordered the vessel abandoned, it emerged automatic devices could not lower containment bars of the remaining reactor. Preminin and another sailor, Lt. Nikolai Belikov, were sent into the hold to lower the bars by hand, Trud said.

The hold was filled with toxic gases and temperatures that reached 158 to 176 degrees.

The two men managed to partially lower the bars before returning, when Lt.

Belikov collapsed.

Preminin went down again and lowered the remaining bars. He became trapped when an iron door to the hold jammed.

Yesterday a local Greenpeace spokesman said there is still much uncertainty over nuclear technology. He claimed many small nuclear accidents involving the US and Soviet Union had gone unreported.

He expressed concern over the sinking, saying it was time important facts about it were made public.

He also raised fears of a dredger bringing the sub to the surface.

Environmentalist and Independent MP Stuart Hayward also said the world still had much to learn about nuclear technology.

"We still have not found a way of dealing with nuclear waste,'' he said, adding: "But I can't say the sinking is high on my list of concerns.''