TIME was running out last night for 116 men trapped in a nuclear submarine as the Russians refused British offers of expert help.

Efforts to save the crew of the Kursk, lying 300ft below the surface of the Barents Sea, were hampered for most of yesterday by rough seas.

It was not clear how much oxygen the crew had left and water appeared to be still leaking into the submarine.

Admiral Vladimir Kuroyedov said the situation was "extremely grave".

Last night, a Russian rescue capsule was trying to dock with a cargo hatch, a manoeuvre made even more difficult because the Kursk is leaning at a sharp angle.

Even if the capsule successfully links up with the sub, it can hold only 20 people at a time and bringing it to the surface could take seven hours.

Such a slow rise is necessary to prevent decompression sickness, the potentially crippling or fatal condition known as "the bends".

It would be a laborious and nerve-fraying process under the best of circumstances, and weather forecasts indicated conditions in the disaster area would be rough for several days.

The navy said the Kursk crashed to the bottom on Sunday during military exercises, but the news agency Interfax reported that the accident happened on Saturday.

Russia has refused offers from the United States and Britain to send trained rescue personnel and equipment, even though the Russian navy lacks sophisticated rescue gear.

Navy spokesman Captain Igor Dygalo said that coordinating the rescue with other countries would take too much time and "we cannot afford to waste it".

Despite this, preparations were being made last night to dispatch a British submersible to the area should the Russians change their minds. The British Government has chartered an aircraft, which was due to arrive at Scotland's Prestwick Airport in the early hours to pick up the submersible.

The vessel, which is under exclusive contract to the Ministry of Defence, is operated by a crew of three and could transfer a maximum of 16 Russian sailors at a time.

An ministry spokesman said: "It is specifically designed for this type of work.

"We are getting ourselves ready so we can move quickly if we get the request." Britain has also offered a survey ship.

A Nato spokesman said half-a-dozen senior Russian military officials in Brussels had a 30 minute teleconference yesterday with Nato experts in London.

The Russians wanted to know what help Nato could provide if a formal request for help was made to the West.

While immediate concerns focused on the crew, there was also worry over whether the accident would result in a leak of radioactive material.

Officials said the Kursk's two nuclear reactors had been switched off and it was not carrying nuclear weapons.

Admiral Kuroyedov said there appeared to have been an explosion in the torpedo compartment in the nose of the submarine, sending it crashing to the sea bottom.

Earlier, he had said the submarine likely had collided with something.

An explosion inside the torpedo chamber, which contains warheads, would probably have caused extensive casualties.

Several compartments inside the submarine were flooded. Submarines are divided into compartments that can be sealed off.

Russian and Western submarines sometimes play cat-and-mouse games in the area and have scraped each other in the past.

The US navy said on Monday it had a monitoring ship in the area, but there was no indication that a US vessel had been involved.

Russian submarines have been involved in a string of accidents in recent decades. The navy is desperately short of money and performs almost no maintenance on its ships