Seoul  - South Korea on Monday protested what it said was the unannounced opening of a North Korean dam's floodgates that led to a wave of water rushing down the Imjin River and sweeping away six South Korean campers who are feared dead.

The incident could spell trouble for ties between the two neighbours, which had been cautiously warming in August.

The Unification Ministry in Seoul said South Korea's government expressed regret at Sunday's incident and requested that the North provide alerts in the future so similar incidents do not happen again.

The release of the water at the dam about 30 kilometres north of the inter-Korean border was apparently deadly for both countries. South Korea's Yonhap News Agency reported that police found the body of a boy, aged 4 or 5, that was believed to have drifted downstream from North Korea.

Unannounced water discharges from North Korean dams have caused flooding and damage in South Korea since 2000 when the North began building the structures, but Sunday's discharge was the first to cause deaths.

It came after North Korea made a series of conciliatory gestures last month, clearing the way for the resumption of reunions of families separated by the 1950-53 Korean War and relaxing restrictions on traffic over the heavily militarized Korean border.

It also announced it would allow South Korean tourists to visit the country again and sent its first envoys to Seoul to meet with President Lee Myung Bak since Lee took office at the beginning of last year. North Korea also released several detained South Koreans, including a manager at the Kaesong industrial park who criticized the North Korean regime. (dpa)