The Washington Post reports:

South Korea will formally blame North Korea on Thursday for launching a torpedo at one of its warships in March, causing an explosion that killed 46 sailors and heightened tensions in one of the world’s most perilous regions, U.S. and East Asian officials said.
South Korea reached its conclusion that North Korea was responsible for the attack after investigators from Australia, Britain, Sweden and the United States pieced together portions of the ship at the port of Pyongtaek, 40 miles southwest of Seoul. The Cheonan sank on March 26, following an explosion that rocked the vessel as it sailed in the Yellow Sea off South Korea’s west coast.
The officials, who spoke on condition of anonymity because South Korea has yet to disclose the findings of the investigation, said that subsequent analysis determined that the torpedo was identical to a North Korean torpedo that had previously been obtained by South Korea.
South Korea’s conclusion underscores the continuing threat posed by North Korea and the intractable nature of the dispute between the two Koreas. South Korean President Lee Myung-bak must respond forcefully to the attack, analysts said, but not in a way that would risk further violence from North Korea, whose artillery could — within minutes — devastate greater Seoul, which has a population of 20.5 million.
South Korea’s report will also present a challenge to China and other nations. China waited almost a month to express its condolences to South Korea for the loss of life, and, analysts and officials said, has seemed at pains to protect North Korea from criticism.
South Korea will request that the U.N. Security Council take up the issue and is looking to tighten sanctions on North Korea, the officials said. The United States has indicated it would support such an action, U.S. officials said. Japanese Foreign Minister Katsuya Okada told his South Korean counterpart on Monday that Japan would do the same, the Japanese press reported Tuesday.