An artillery shell landed in the demilitarized zone south of the military demarcation line around 3 p.m. on Sunday. It had been mistakenly fired by an Army unit in Paju, Gyeonggi Province.
According to the military, the unit was conducting an emergency drill in its compound prompted by North Korea's shelling of Yeonpyeong Island last week. An artillery man who mistook the drill for real combat fired the 155-mm shell, which has a range of 22 km.
It flew 14 km north to land on a hill on the southern side of the demilitarized zone, only 200 m from the military demarcation line. No casualties were reported, but the incident could have led to conflict between two Koreas.
The sudden sound of cannon also startled locals into inundating Army units and government offices with phone calls.
The Defense Ministry notified the North of the mistake through military communication lines about two hours after the incident.