A US soldier is believed to have been detained in North Korea after crossing the border during a visit to the demilitarized zone (DMZ) that separates the country from its southern neighbor, Washington officials said on Tuesday, AFP reported.

“A visiting U.S. service member voluntarily and without authorization” crossed the demarcation line (DMZ), said Col. Isaac Taylor, a spokesman for U.S. forces in South Korea.

Another US official previously told AFP on condition of anonymity that the soldier was likely being held in North Korea.

According to the American television channel CBS, the soldier was supposed to be sent to the United States for disciplinary reasons, but he managed to leave the airport and join a group of visitors to the DMZ.

A few hours earlier, the UN command post said he was in the “Common Security Area” and referred to him simply as a “US citizen” without specifying his military status.

South Korea’s Defense Ministry declined to comment.

“The man let out a loud ‘ha ha ha ha’ and ran through the buildings” after the group he was a part of visited one of the buildings at the site, a witness told CBS News.