SEOUL — An external blast appears to have caused the sinking of a South Korean warship near the disputed North Korean border three weeks ago, a chief investigator said Friday.
"The possibility of an external explosion is far higher than that of an internal explosion," Yoon Duk-Yong, the co-head of a state investigation team, said at a televised news conference.
He said his assessment was based on an initial on-site probe launched Thursday after the battered stern of the sunken 1,200-tonne corvette the Cheonan was recovered from the Yellow Sea this week.
Defence Minister Kim Tae-Young, who has raised the possibility that a mine or torpedo may have hit the warship, said the government regards the sinking as "a grave national security incident".
Seoul has not so far accused Pyongyang of involvement but the incident has raised cross-border tensions.
A total of 46 sailors lost their lives in the March 26 disaster, the deadliest peacetime naval tragedy for South Korea.
A giant floating crane on Thursday lifted the stern section of the Cheonan which was split in two last month by what survivors described as a big external explosion.
Military officials said 36 bodies of men mostly in their 20s had been found from the stern after two bodies were recovered earlier in the month. A total of 58 crewmen were rescued soon after the sinking.
Yoon said 38 civilian and military investigators including two US experts had examined the stern of the Cheonan.
"Judging from damage to the ship's external wall, we believe the probability of an internal explosion is very low," he said, adding the chances of metal fatigue or an underwater obstacle were also slim.
Defence minister Kim called for patience but warned that said the military would take "stern" action against whoever is found to be responsible.
South Korea has launched an international investigation into the disaster to ensure the eventual findings cannot be disputed.
The probe, which could take weeks, involves more than 120 local experts, eight Americans and three Australians, the defence ministry said. Four experts from Sweden were to arrive later.
The bow section of the ship is expected to be raised in about 10 days.
"The remaining task is to find the cause of the incident through a scientific and fair probe," Prime Minister Chung Un-Chan said Friday.
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 that left a North Korean patrol boat in flames.