SYDNEY ? Australia called off an air and sea search for survivors on Wednesday after a boat carrying unidentified Sri Lankans sank in remote seas far off its northwest, killing 12.

Home Minister Brendan O'Connor said there was no hope of finding anyone else alive after the boat carrying 39 went down in stormy conditions overnight Sunday, sparking frantic rescue efforts by passing ships and Australian planes.

"Medical advice received indicates that there is no further chance of survivability," O'Connor said in a statement. "This is a tragic incident."

Some 27 male survivors plucked from the sea by the Bahamas-registered LNG Pioneer tanker, along with one body, will be taken to Christmas Island ? Australia's main asylum-seeker processing centre.

However, Prime Minister Kevin Rudd said the status of the survivors was unknown. Australia has intercepted dozens of boats carrying more than 1,700 asylum-seekers, many of them Sri Lankans, and Afghans, this year.

"It's been some time since the vessel sank. Of course it's a great tragedy... it's just an awful set of circumstances," Rudd told Fairfax radio.

The boat got into trouble late on Sunday some 2,700 kilometers (1,700 miles) from Australia's northwest in the Indian Ocean and sank during a rescue attempt by the LNG Pioneer and a fishing boat, officials said.

Asylum-seekers have returned as a major political issue in Australia this year after a sharp rise in arrivals, with critics blaming Rudd's softening of the tough policies of his conservative predecessor, John Howard.