A Russian mini-submarine carrying seven sailors snagged on a fishing net and was stuck 625 feet down on the Pacific floor Friday.
A Russian vessel attempted to tow the stranded sub to shallower waters as the United States and Britain rushed unmanned vehicles there to help in rescue efforts.
It was unclear whether there was enough oxygen aboard the mini-sub to keep the crew alive long enough for remote-controlled vehicles to reach them from bases in San Diego and Britain.
A Russian rescue vessel snagged the mini-submarine with a cable and was trying to drag it to shallower waters, Pacific Fleet commander Adm. Viktor Fyodorov told NTV television Saturday by telephone.
"We have hooked onto the whole system that our bathyscaph is in," Fyodorov told NTV. A bathyscaph is a deep-sea diving apparatus.
Fyodorov said there was enough oxygen to keep the crew alive for at least 18 hours. Interfax earlier quoted him as saying the air supply would last until Monday.
The Russian sub's propeller became entangled in a fishing net Thursday, navy spokesman Capt. Igor Dygalo said on state-run Rossiya television. The accident occurred in Beryozovaya Bay, about 50 miles south of Kamchatka's capital, Petropavlovsk-Kamchatsky, officials said.
"There is air remaining on the underwater apparatus for a day _ one day," Dygalo said at about 6 a.m. EDT. "The operation continues. We have a day, and intensive, active measures will be taken to rescue the AS-28 vessel and the people aboard."
It was unclear where the net came from, but scientists say the Pacific is rife with "ghost nets"-- sometimes miles-long nets that have detached from fishing trawlers and now drift in the ocean.
Fleet spokesman Capt. Alexander Kosolapov said contact had been made with the sailors, who were not hurt.
The mini-sub, called an AS-28, initially was too deep to allow the sailors to swim to the surface on their own or divers to reach it, officials said. However, dragging the sub into shallower waters could make such an escape or rescue possible.
The crisis evoked comparisons with the 2000 disaster involving the nuclear submarine Kursk. The Kursk sank to the bottom of the Barents Sea after explosions on board, killing all 118 seamen aboard.
However, some Kursk sailors survived for hours as oxygen ran out, and President Vladimir Putin was criticised severely for waiting several days before asking for international assistance. Also, Russian divers discharged by the navy for lack of funds said at the time their own offers to help were rebuffed.
This time, Russia waited just a day before seeking help.Both accidents raised questions about the state of Russia's cash-strapped military. The same type of vessel that is now stuck, called a Priz, was used in the rescue efforts that followed the Kursk disaster, Interfax reported.
The latest accident occurred early Thursday after the mini-submarine was launched from a rescue ship during a combat training exercise, Kosolapov said. The AS-28, built in 1989, is about 44 feet long and 19 feet high and can dive to depths of 1,640 feet.
Russia appealed to the United States and Japan for assistance, the Interfax news agency quoted Foreign Ministry spokesman Boris Malakhov as saying.
The US Navy was loading two robotic rescue vehicles aboard a massive C-5 transport plane at Naval Air Station North Island near San Diego for the flight to Russia. The loading started at 1:45 p.m. EDT and was expected to take several hours, officials said.
"When we got word, the Russians were in need, we were more than happy to help out a friend," said US Air Force Lt. Ryan Lindsay, the C-5 pilot.
The unmanned vehicle, called a Super Scorpio, can reach depths of up to 5,000 feet and is equipped with high-powered lights, sonar and video cameras, said Capt. Matt Brown, a spokesman for the US Navy's Pacific Fleet in Honolulu.
The Super Scorpio then will be transported by truck and loaded on a Russian ship before making its descent to the stricken vessel.
Brown said the Russian military has indicated that the AS-28 may have been fouled by fishing nets or steel cables. The Super Scorpio has an instrument that can cut 1-inch-thick steel cables, he said.
The Super Scorpio, which weighs about 4,500 pounds, has been used to conduct underwater surveys and inspections.
About 30 people will accompany the vehicle to Russia, Brown said."We are working as fast as we can to make this happen," he said.
The British vehicle was being loaded onto a Royal Air Force transport plane at Scotland's Prestwick airport and was expected to arrive at Petropavlovsk-Kamchatsky, the city nearest the site, at about 5 a.m. Saturday, said Anton Atrashkin, spokesman for the British Embassy in Moscow.
That means the British vessel likely will arrive before the U.S. vessel.
Since Soviet times, the Kamchatka Peninsula has housed several major submarine bases and numerous other military facilities, and large areas of it have remained closed to outsiders.
Airlifting a US underwater vehicle to the area will mark the first time since the World War II era that a US military plane has been allowed to fly there.
At Moscow's request, Japan dispatched a vessel carrying submarine rescue gear and three other ships to join salvage efforts, but they were not expected to arrive at the scene until early next week, Marine Self Defense Force spokesman Hidetsubu Iwamasa said.
Since the Soviet collapse, the Russian navy has struggled to find funds to maintain and repair its ships and has had to scale back its modernisation programme.
After the Kursk disaster, Putin called for serious improvements in the military's equipment and training, but little improvement has been noticed publicly.
(Associated Press reporters Robert Burns in Washington and Greg Risling in Los Angeles contributed to this report.)