On Saturday, the United States and Britain had special underwater vehicles on their way to the site of the accident, off the Kamchatka peninsula in Russia's far east. However, time was running out for the crew, 190m down on the ocean floor, who had limited air supplies left.

Conflicting official accounts of the incident involving the AS-28 mini-submarine have drawn uncomfortable comparisons with the Kursk nuclear submarine disaster five years ago.

All 118 men on board the Kursk, which sank in the Barents Sea in August 2000, died after a botched rescue, over which President Vladimir Putin was fiercely criticised at home for failing to call for international help sooner.

"We must complete the operation in 24 hours because the supply of air on board is not without limit," Interfax news agency quoted the deputy chief of navy staff, Vladimir Pepelyaev, as saying.

The AS-28 is a deep-water rescue
submersible vehicle (frame grab)

"It is believed that there is still enough air for slightly more than 24 hours," Pepelyaev said.

Initial official reports said the AS-28, itself a rescue vessel, ran into trouble when its propeller became entangled in fishing nets during a military exercise. They said it had five days' supply of air - more than enough for any rescue mission.

24 hours

However, about 1000 GMT on Friday, naval spokesman Igor Dygalo said the trapped vessel had only 24 hours' worth of air left. There was no official explanation why estimates of air remaining still stood at 24 hours on Saturday morning.

Later, Pacific Fleet commander Admiral Viktor Fyodorov said the AS-28 had been ensnared by a large antenna, part of an underwater electronic station, rather than a fishing net.

Late on Friday, rescuers tried to drag the stricken vessel closer to shallow waters to allow the crew to escape, but the operation was called off.

"At the moment, the operation has been halted," Pepelyaev said.

Minimising movement

Officials said the crew was in a satisfactory condition and they were trying to conserve oxygen by keeping their movements to a minimum.

Officials said the navy was not ceasing rescue operations but was increasingly pinning its hopes on British and US rescuers, brought to the scene at Russia's request.

A British Scorpio underwater rescue vessel - a remote-controlled vehicle capable of descending 925m - was airlifted at about 0600 GMT to Kamchatka, the RIA news agency reported. It will take up to six hours for it to reach the scene.

US navy sailors prepare to load a
Super Scorpio on to an aircraft

Interfax news agency later reported from Petropavlovsk-Kamachatsky that a US transporter with an unmanned deep-diving Super Scorpio submersible had landed.

Interfax said two more US planes with rescue equipment were expected at about 1100 GMT.

Japan has sent four military vessels, but they would arrive only in three or four days' time.

The Russian press, enjoying some independence from Kremlin control, drew comparisons between the Kursk rescue efforts and the Kamchatka operation.

"Very much like it was five years ago, the naval command was slow in reporting the incident and then insisted for a long time that the sailors had enough air and food, that there was good communications with them," the newspaper Kommersant wrote.

"Very much as with the Kursk, direct work to save the submersible started more than a day after the incident occurred," it added. "In both events, the navy proved it is not prepared for the operation because of lack of experts and faulty equipment."