A North Korean who crossed the heavily fortified land border into the South has been detained and taken into custody, Seoul’s military said Friday.

The North Korean, identified as a male civilian, managed to cross the Military Demarcation Line (MDL) in the midwestern part of the Demilitarized Zone (DMZ) on Thursday, Seoul’s Joint Chiefs of Staff said.

The MDL is the de facto border, which runs through the middle of the DMZ — the border area separating the two Koreas, which is one of the most heavily mined places on earth.

“The military identified the individual near the MDL, conducted tracking and surveillance,” the Joint Chiefs of Staff, or JCS, said in a statement.

It then “successfully carried out a standard guiding operation to secure custody,” it added.

The operation took about 20 hours, according to Seoul, after the man was detected by a military surveillance device sometime between 3 and 4 a.m. local time Thursday.