A narrow slab of concrete, seen from above, marking the border between South and North Korea sits across a walkway with gravel on one side, dirt on the other and a blue wall behind it.

A concrete slab marking the Military Demarcation Line is pictured from the North Korean side of the Joint Security Area. (Aaron Kidd/Stars and Stripes)

SEOUL, South Korea — A North Korean soldier was taken into custody by the South Korean military Thursday after crossing the heavily fortified border between the two Koreas, according to the South’s Ministry of National Defense.

The unidentified North Korean soldier crossed the Military Demarcation Line — the actual border dividing the Korean Peninsula — Thursday evening, the ministry said in a text message to news reporters the next day.

The message did not mention the soldier’s motive for crossing the border.

No unusual actions by the North Korean military were detected after the soldier was taken into custody, the ministry added. The soldier will be investigated by law enforcement agencies.

This story will be updated.