An American soldier has been detained in North Korea after crossing the Military Demarcation Line, according to a senior U.S. official who spoke to Fox News.

The incident took place during a tour of the joint security area between North and South Korea, where the individual reportedly crossed the line without authorization.

The U.N. Command confirmed the unauthorized crossing, saying the U.S. national is now believed to be in custody in North Korea. Efforts are underway to resolve the incident, with the peacekeeping force working alongside their Korean People’s Army counterparts, according to the Fox report.

As of now, the identity of the detained soldier remains unknown.