The South Korean military says it captured a North Korean civilian late Thursday, after he crossed the heavily fortified land border between the two Koreas.

According to Seoul’s Joint Chiefs of Staff, military devices initially detected the man between 3 and 4 a.m. Thursday at a stream along the military demarcation line in the midwestern part of the Demilitarized Zone.

During an operation that lasted over 20 hours, the South Korean troops pursued and monitored the man, who was mostly motionless during the day.

The troops approached him as he began to move at night, telling him to follow their instructions and guiding him to safety south of the border.

At the time of the contact with the military, the man identified himself as a civilian and said he was unarmed.

He has since been transferred to the relevant authorities for an investigation.

The military says it has yet to detect any unusual signs from the North Korean troops and has informed the United Nations Command of the incident.