WASHINGTON — The US will investigate why a South Korean warship sank near the disputed border with North Korea before seeking to jumpstart nuclear talks with Pyongyang, a US official said Wednesday.

"Let's find out what happened in the sinking of the corvette," Assistant Secretary of State for East Asian and Pacific affairs Kurt Campbell said when asked by reporters to comment on moves to revive six party talks to end North Korea's nuclear weapons drive.

"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," he said.

Campbell said he visited South Korea last week and offered "every assistance in trying to recover both the remains and parts of the ships to ascertain what transpired in terms of how that ship was tragically sunk."

North-South tensions have been high since an unexplained explosion sank a South Korean warship near the disputed Yellow Sea border on March 26, and after the North scrapped a tourism deal with the South.

The South has not so far accused the North of involvement in the blast. Its defense minister has raised the possibility that a mine or torpedo may have torn the 1,200-tons corvette in two with the loss of 46 lives.

The bodies of most of the crew are believed trapped in the stern.

The area around the disputed border was the scene of deadly naval clashes between the North and South in 1999 and 2002 and of a firefight last November.

Sailors who survived the disaster have said a big external blast tore the ship apart, discounting theories that it sank during an explosion on board or a grounding.

On the North Korea nuclear talks, Campbell said the United States and South Korea would have to agree on any "next steps" on that diplomatic drive.

"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.

"So we want to coordinate very closely vis-a-vis North Korea."

North Korea last year stormed out of six-nation talks in which it had agreed to end its nuclear program in return for security guarantees and aid.

It declared void the agreements from the talks, that also included the United States, China, Japan, South Korea and Russia, but later promised to return to the table after an appeal by Beijing.

But Pyongyang has since balked and insisted the United States first sit down to hammer out a peace treaty, which could effectively validate leader Kim Jong-Il's rule. The 1950-53 Korean War ended only with an armistice.

President Barack Obama said on Tuesday that North Korea has "chosen a path of severe isolation that has been extraordinarily damaging to its people."

"It is our hope that as pressure builds for North Korea to improve its economic performance... that we'll see a return to the six-party talks and that we will see a change in behavior," Obama said.

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