The South Korean military maintained its highest alert level against North Korea all day Monday, even though police prevented activists from floating propaganda leaflets across the border.
Pyongyang earlier threatened to attack the Imjingak pavilion overlooking the border if activists went ahead with their plan to float propaganda leaflets across the border from there.
North Korean artillery batteries on the western frontline, which can strike the area, were reportedly on alert until the afternoon.
"North Korea's frontline artillery batteries forward-deployed self-propelled guns, towed howitzers and personnel at fire positions from yesterday until this afternoon," a South Korean military source said. "They relaxed their alert posture late in the afternoon."
The source added the military here will remain on alert.
North Korean frontline divisions have artillery such as 122 mm and 152 mm self-propelled guns and towed howitzers, and 122 mm multiple rocket launchers.
But a source said the North Koreans did not roll their 170 mm self-propelled guns and 240 mm multiple rocket launchers out of the caves where they are kept.
The South Korean artillery units also put state-of-the-art fighter jets including the F-15Ks in position. An army corps in charge of defending the Imjingak area deployed K-9 self-propelled guns with a range of 40 km and multiple launch rocket systems.