SEOUL, Aug. 16 -- For the first time this year, South Korean forces fired warning shots along the most heavily fortified border on earth. The soldiers who triggered them were North Korean, apparently on a routine patrol that drifted across an invisible line in the eastern stretch of the Demilitarized Zone. They withdrew when the shooting started. Nobody died.

South Korea's Joint Chiefs of Staff confirmed the incident on Saturday, with Yonhap, the state news agency, citing unnamed military officials. The crossing occurred sometime last week in the eastern section of the DMZ. After warning fire, the North Korean soldiers retreated across the Military Demarcation Line. Yonhap reported that "no other unusual military activity" followed their...