The Times of London picks up a report from Yonhap News that will put the two Koreas into a dangerous confrontation.  An investigation into the sudden explosion and sinking of South Korean corvette Cheonan has concluded that the ship was struck by a torpedo amidships.  Calling this “clearly the work of North Korea’s military,” the conclusion will force Seoul into some sort of retaliation — which could touch off another war on the peninsula:

Last month’s deadly sinking of a South Korean naval ship was caused by a North Korean torpedo, a news report said today, adding to pressure on the South’s President. Lee Myung Bak, to respond to one of the worst acts of military provocation since the Korean War.

The South Korean defence ministry declined to comment on the claim by the Yonhap news agency, the latest in a series of reports suggesting that the mysterious sinking of the naval corvette, Cheonan, on March 26 was a deliberate and unprovoked attack by North Korea.

Forty-six sailors are dead or missing after the attack, which cut the 1200-tonne vessel in two. But President Lee’s Government appears to be struggling to find an appropriate response, which will demonstrate its resolve in the face of aggression, but stop short of a costly and unpredictable war.

That may not be the last word on the cause, although the motive remains clear. The probe also considers the possibility of a suicide attack by submarine on the ship, prompted by a clash in November whose outcome embarrassed Pyongyang and its military. The Chosun Ilbo newspaper reported that the DPRK plotted its revenge by training “human torpedoes,” which may seem a little far-fetched but still possible. A standard torpedo launch would have been tracked by other ships, whereas a suicide (or remote controlled) submarine vessel could have remained undetected until detonation.

Lee won his election by promising a get-tough policy with Kim Jong-Il, saying that he would shoot three or four bullets back at Kim for every two sent their way. Now he has his opportunity to put that toughness on display, but it’s a delicate balancing act. Almost any kind of military retaliation would result in war, for which Seoul may be more prepared but still extremely vulnerable. Any kind of large-scale military action will leave tens of thousands dead, and missiles will rain down on the South almost from the start.

Lee also has to weigh the amount of support he can expect from the US if the Korean War reignites, especially from an act by Seoul against the North. Would Barack Obama take action against Kim under those circumstances? Or would the US back away from its security obligations, especially considering the close financial relationship between the US and China? Don’t expect to see anything too aggressive, as Lee most likely doesn’t want to discover the answer to those questions.