North Korea torpedoed South's navy ship - report

South Korea's military believes a torpedo fired from a North Korean submarine sank its navy ship last month, based on intelligence gathered jointly with the United States, a news report said today.

The Yonhap news agency report appears to be the clearest sign yet that Seoul blames Pyongyang for the sinking, thought to have killed 46 sailors in what would be one of the deadliest incidents between the rivals since the end of the 1950-53 Korean War.

The military's intelligence arm sent the report of "certain" North Korean involvement to the presidential Blue House soon after the incident, Yonhap quoted a high-ranking military source as saying.

The report could be an embarrassment to South Korean President Lee Myung-bak, whose government has come under criticism for its handling of the incident.

"North Korean submarines are all armed with heavy torpedoes with 200 kg (441 lb) warheads," the military source was quoted as saying by Yonhap. "It is the military intelligence's assessment that the North attacked with a heavy torpedo.

"The military intelligence has made the report to the Blue House and to the Defence Ministry immediately after the sinking of the Cheonan that it is clearly the work of North Korea's military," the source was quoted as saying.

South Korea plans to soon raise the front half of the 1,200-tonne Cheonan, which went down near a disputed sea border with North Korea, and will issue its verdict on the cause of the explosion that sank the warship after that.

Analysts said there is little South Korea can do even if Pyongyang is found to be the culprit, because a military response was likely to hurt its own quickly recovering economy and bolster North Korean leader Kim Jong-il's standing at home.

The reclusive North has denied it had anything to do with the sinking near the disputed sea border off the west coast that has already been the scene of two deadly naval battles in the past decade.

It accused Lee of using the incident for political gains ahead of crucial local elections in June.

Yonhap said the South Korean and U.S. military suspected the North was stepping up drills to infiltrate a submarine south of the naval border, hidden among Chinese fishing boats, and wage a surprise attack against the South.