South Korea's navy on Wednesday was trying to raise a suspected North Korean submarine from the sea bed, but defense ministry officials said none of the vessel's crew was likely to have survived.

"It is highly unlikely to see the North Korea crew come out of the sub alive," said Capt. Oh Se-yuong, who led the towing operations in the northeastern port city of Donghae."But we cannot completely rule out the possibility of survival," he told Reuters.

Ministry officials said the 82-foot Yugo-class submarine must surface two to three times a day to recharge its oxygen.

"The sub has not had a chance to recharge air since Monday afternoon. I don't think there will be survivors by the time now," said Maj. Kim Jung-woo, a spokesman for Seoul's Joint Chiefs of Staff.

The navy is trying to bring the midget sub to a naval dockyard in Donghae by the end of the day, a ministry official said. It sank on Tuesday while being towed to port by a South Korean warship.

"So far, all operations look OK. We will be able to raise the sub as early as this evening," said Oh.

Ministry officials said about 100 navy divers were working on the recovery operation.

Under current plans, the sub would be moved onto land in the dockyard on Thursday for investigation, the ministry said.