The North's soldiers briefly crossed the military demarcation line in the central section of the DMZ around 11 a.m. local time (02:00 GMT) on Thursday but returned to the North's side as the South's military fired warning shots, the report said.
The report cited a JCS official as telling journalists that the incident appeared to be accidental as the North's soldiers continued working into the night after they returned to North Korea's side of the border.
"Similar situations may occur going forward as North Korean soldiers are carrying out the activities across several locations within the DMZ," Yonhap quoted the official as saying.
The incident marked the third border violation by North Korean soldiers this month, following two similar incidents on June 9 and June 18, respectively. The report cited the JSC as saying that both cases also appeared to be unintentional.