A South Korean naval ship sank in the Yellow Sea near the border with North Korea late on Friday, and more than 40 sailors are missing while 58 were rescued, local media reported.
The incident involving the Cheonan vessel forced South Korean President Lee Myung-bak to convene an emergency security meeting although there was reportedly no sign that North Korea was involved. Patrol boats and helicopters were deployed for a rescue operation.
The Navy, as quoted by the Yonhap news agency, said it has been "unable to pinpoint the exact cause of the incident" so far. Reports said an explosion in the ship's rear could have ripped a hole in its bottom.
The border between the two Koreas was unilaterally drawn by the U.S.-led United Nations Command in the wake of the 1950-1953 Korean War and has been a sticking point between the North and the South.
Pyongyang has not acknowledged the borderline and has drawn a new one on its own south of the current border. Naval clashes between the two states over the disputed area took place in 1999, 2002, 2009 and this year.
The two countries remain technically at war as their conflict ended only in an armistice in 1953.
MOSCOW, March 27 (RIA Novosti)
