A planned launch of balloons by South Korean activists to send leaflets to North Korea on Saturday with messages critical of its leader turned into a clash with residents of the border area who said the move will threaten peace between the two countries.

Hundreds of residents of the city of Paju near the heavily militarized border turned up in a show of force, many elderly farmers and some driving tractors aimed at blocking roads, to try and stop the launch of the leaflets by anti-North groups.

North Korea has threatened unspecified "military action" if the launch were to be allowed by South Korean authorities and said it could scuttle planned inter-Korean talks aimed at easing tensions and improve ties.