SEOUL — Salvage crews lifted the stern of a shattered South Korean warship from the seabed Thursday, a move which could provide clues to its mysterious sinking near the North Korean border almost three weeks ago.

Live television showed a giant floating crane raising the stern section of the 1,200-tonne corvette, which was split in two by what survivors described as a big external explosion on March 26.

The bodies of most of the 46 crewmen killed in the disaster are believed still trapped in the stern of the Cheonan, which was later to be hoisted onto a barge and taken to a naval base at Pyeongtaek south of Seoul for inspection.

More than 120 local experts, along with seven Americans and three Australians, will investigate the sinking -- a process which could take weeks.

The disputed Yellow Sea border was the scene of deadly naval clashes between the North and South in 1999 and 2002 and of a firefight last November which left a North Korean patrol boat in flames.

Seoul's defence minister has raised the possibility that a mine or torpedo may have hit the Cheonan. The government has not so far accused Pyongyang of involvement but the incident has raised cross-border tensions.

KBS television showed navy Seals and hard-hatted salvage workers standing on the deck as the stern was lifted partially above the surface. They rigged a huge net across the severed edge of the hull to stop debris falling out.

"It seems that the ship was broken apart by a very powerful impact," former navy admiral Ahn Ki-Seok told the TV station. The superstructure above the severed edge appeared badly damaged.

Water which failed to drain from the stern was being pumped out. The bodies were expected to be recovered by Thursday evening and would be taken to a morgue by helicopter from a nearby naval ship.

President Lee Myung-Bak has called for "a very objective investigation" whose findings cannot be disputed, and promised "stern measures" against whoever was to blame.

The sinking may have sunk hopes for an early resumption of six-party talks on North Korea's nuclear disarmament, a senior US official said Wednesday in Washington.

"Let's find out what happened in the sinking of the corvette," Assistant Secretary of State Kurt Campbell said when asked by reporters about moves to revive the talks.

"At this juncture, we told our South Korean friends that our primary objective is to work with them on the recovery of the ship and at that point, we will be able to make some judgments about the way forward."

Campbell said the United States and South Korea would have to agree on any next steps on restarting the talks.

"We want to be very clear that there is a complete agreement between South Korea and the United States about next steps, if there are to be next steps given recent developments," he said.

The North quit the nuclear talks a year ago.

As preconditions for returning, it wants a US commitment to discuss a permanent peace treaty and the lifting of UN sanctions. Washington says it must first return to the nuclear forum and show seriousness about negotiating.

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