SEOUL - South Korea proposed on Monday holding talks with the North on preventing flooding from a river flowing across their border that killed six South Koreans last month when the communist state released a surge of water without warning.

The proposal is part of a series of working-level contacts between the rivals, whose ties have remain chilled since President Lee Myung-bak came to office in the South last year and ended a decade of free-flowing aid for its impoverished neighbor.

The six were swept away by a surge of water in the middle of the night in early September while camping on the banks of the Imjin River.

North Korea said it had no choice but to open flood gates at its dams because of rising water levels. South Korea has rejected that explanation, saying there were no indications of dangerous water level rises.

South Korea for years has worried about dams the North has built along rivers flowing across the border, fearing its communist neighbor could use flood waters as a weapon.

The North has built several dams on the Imjin River, a major waterway, including one a few kilometres north of the heavily armed border between the two states, who have yet to sign a formal peace treaty to end the 1950-53 Korean War.

South Korea has long sought the North's cooperation in flood control and setting up warning systems but Pyongyang has been reluctant to join such efforts.

(Reporting by Jack Kim; Editing by Jonathan Hopfner)

South Korea