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 on Thursday.
The Yonhap news report appears to be the clearest sign yet that Seoul believes Pyongyang is to blame for 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 March 26 incident, Yonhap quoted a high-ranking military source as saying.
Also Thursday, the mass-circulation Chosun Ilbo newspaper reported that military intelligence officers warned earlier this year that the North was preparing a suicide submarine attack on a South Korean vessel in retaliation for an earlier defeat in a sea battle.
Seoul has not publicly blamed Pyongyang for the blast, and the North has denied involvement, but suspicion remains given the country's history of provocation and attacks on the South.
President Lee Myung-bak's government has come under criticism for what many see as its overly cautious handling of possible links to North Korea. It has called for a thorough investigation of the sinking, thought to have killed 46 sailors.
Market players have been calmed by the South's measured response, seeing Seoul as unlikely to take aggressive moves that would escalate into armed conflict and harm the export-driven economies of North Asia, responsible for about one-sixth of the global economy.
South Korea's defense ministry had no comment on the Yonhap report.
"North Korean submarines are all armed with heavy torpedoes with 200 kg (441 pound) 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 Defense 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.
Military response unlikely?
South Korea plans to soon raise the front half of the 1,200-ton Cheonan, which went down near a disputed sea border with North Korea, and will issue its verdict on the cause of the explosion 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.
Lee ended a decade of no-questions-asked aid to the destitute North and called for a hard-line push for Pyongyang to disarm.
"The nuclear issue has still not been resolved. This and the Cheonan incident all serve to inflict a negative impact on the Lee administration," said Lee Nam-young, a political analyst at the Sejong University in Seoul.
The reclusive North has denied it had anything to do with the sinking near the disputed sea border off the west coast that has 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.
Suicide attack?
On Thursday, the Chosun Ilbo newspaper reported the Korea Defense Intelligence Command alerted the navy weeks ahead of the ship sinking that North Korea was preparing underwater suicide teams in mini-submarines to attack the South.
These "human torpedo" squads were said to involve small submarines navigated so close to the target that their torpedoes or explosives blow up both target and the attackers, or are timed to explode while the attackers escape from the vehicle, the report said.
The attack preparations were aimed at retaliating against the South over its defeat in a naval skirmish in November, the paper said. The site of the sinking is near where the rival Koreas fought three times since 1999, most recently a November clash that left one North Korean soldier dead and three others wounded.
The two Koreas have never signed a peace treaty since the Korean War ended in 1953 in a truce.
The Chosun Ilbo said the military was investigating whether the navy and Joint Chiefs of Staff had been properly braced for a North Korean attack following the intelligence warning, though it's not clear whether the Cheonan sank because of an attack.
Navy and Joint Chiefs of Staff officials said they would not comment on the report because it involves military intelligence affairs.
A high-profile North Korean defector living in Seoul said he believes Kim masterminded the blast to stoke tension, cause social confusion in the South and shake its economy.
"It's obvious it's something that Kim Jong-il did. We already know Kim Jong-il has been preparing for this kind of incident," said Hwang Jang-yop, a former secretary of the North's Workers Party who once mentored Kim before defecting to Seoul in 1997, in an interview with Chosun Ilbo published Thursday. He didn't provide any evidence for his belief.
A Seoul-based activist said Thursday that he also believes Kim is behind the attack, citing an unidentified North Korean military officer as saying the leader visited a west coast naval command in February and called for revenge for the earlier defeat. Choi Sung-yong told reporters the officer told him a North Korean semi-submersible vessel torpedoed the Cheonan.
Two North Korean agents were arrested Tuesday for allegedly plotting to assassinate the 87-year-old Hwang, who has openly condemned Kim's regime as totalitarian.