South Korea is commemorating the 10th anniversary of a deadly naval clash with North Korea.

South Korean President Lee Myung-bak attended Friday's ceremony at a naval base south of Seoul and vowed stern punishment for any future North Korean attacks.

Six South Korean sailors died in the 2002 incident, while North Korea's casualties are unclear.

North Korea disputes the maritime boundary with South Korea, and the rivals' navies have fought three deadly skirmishes off their west coast since 1999. In 2010, North Korea bombarded a South Korean front-line island near the western boundary, killing four South Koreans.

The Korean Peninsula is still technically in a state of war because the 1950-53 Korean War ended in a truce.