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.