South Korea’s military said Sunday that an unidentified person crossed the eastern inter-Korean border into North Korea.

South Korea’s Joint Chiefs of Staff said an individual was spotted crossing the Military Demarcation Line at around 9:20 p.m. Saturday, through surveillance equipment installed in the border region.

The JCS added it confirmed the person crossed the border at 10:40 p.m., some 80 minutes after the military immediately deployed its unit to locate the person.

The JCS said it sent a message to North Korea to inform it of the border crossing incident, but it has not received a response yet.

The JCS added it cannot identify the person or verify that the person is alive or not at this moment. The JCS noted that an investigation was underway, and more details were expected to come.

Meanwhile, the military is expected to face criticism over the security lapse and delayed response to the incident.

According to South Korea’s military‘s announcement, the unidentified person’s attempt to cross the border was first detected at around 6:40 p.m. through the general outpost barbed-wire fence equipped with motion-detecting sensors.

The military unit responsible for the sector, however, was not aware of the circumstance and made no follow-up measures.

The defection could also call into question the South Korean military’s ongoing efforts to strengthen its border defense system, with enhanced surveillance equipment, which followed a series of border crossing incidents in recent years.

In February last year, a North Korean man swam ashore into South Korea undetected. In November 2020, another North Korea civilian defected into the South but was found some 14 hours after he initially crossed the border.