MOSCOW, Russia — The U.S. Navy says it is sending a crew to Russia’s Pacific Coast to rescue seven Russian sailors trapped in a mini-submarine.

The rescue effort is a race against time because the seven sailors are believed to have less than 24 hours of oxygen left.

The AS-28 mini-submarine, itself a rescue vessel, ran into trouble on Thursday when it became snagged by fishing nets and some sort of cable during a military exercise off the Kamchatka peninsula.

The sailors cannot leave the vessel because it is too deep at 190 meters (623 feet) below the surface, according to a Russian Navy spokesman.

A high-level overnight meeting of U.S. Naval officials in Hawaii decided to send a Navy crew from San Diego and an unmanned vehicle called a Super Scorpio to the Pacific waters, U.S. Navy sources told CNN.

The crew and the vehicle will then be taken to a Russian surface ship, from which the crew will drop the vehicle over the side.

They will try to untangle the mini-sub from the fishing nets, the Navy sources said.

Russia swiftly requested assistance from the United States and Japan after the sub became struck.

As the operation geared up on Friday, naval officials revised earlier assertions that the crew had air to last several days.

“There is air remaining on the underwater apparatus for a day — one day,” Capt. Igor Dygalo said Friday on state-run Rossiya television.

“The operation continues. We have a day, and intensive, active measures will be taken to rescue the AS-28 vessel and the people aboard,” he said.

Dygalo and other officials had said earlier the mini-submarine had enough air to last for five days. The confusion was apparently caused by the fact that seven people were on the vessel, which normally carries a crew of three.

The vessel, called a bathyscaphe — a kind of mini-submarine — was in the Berezovaya Bay, about 70 kilometers (43 miles) from Petropavlovsk-Kamchatsky, Russian news agencies reported.

A camera sent down in the water showed that during a dive, the vessel’s propeller became stuck in a fishing net, snagging further when the crew tried to free it, said Dygalo. Some kind of cable or wire was also involved, he said.