North Korean troops “recently” crossed the Military Demarcation Line (MDL) in the eastern sector, prompting South Korean soldiers to fire warning shots, South Korea’s military said Friday.

It marks the second such crossing in weeks along the heavily fortified inter-Korean border, and the military said its troops responded in line with standard operational procedures. There were 17 reported cases of North Korean troops crossing the MDL last year alone.

“Our military is closely monitoring the movements of North Korean troops while maintaining a firm military readiness posture,” the ROK Joint Chiefs of Staff (JCS) said in a statement provided to