In this photo taken on May 9, South Korean soldiers stand guard as they face North Korea in the Joint Security Area of the Demilitarized Zone separating North and South Korea.

Anthony Wallace/AFP via Getty Images

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Anthony Wallace/AFP via Getty Images

In this photo taken on May 9, South Korean soldiers stand guard as they face North Korea in the Joint Security Area of the Demilitarized Zone separating North and South Korea.

Anthony Wallace/AFP via Getty Images

A U.S. man is believed to be in custody in North Korea after crossing the border without authorization, according to the United Nations body that oversees the Demilitarized Zone between North and South Korea.

A Pentagon official who spoke to NPR on the condition of anonymity confirmed that the man was a U.S. soldier in civilian clothes.

He was touring the Joint Security Area, a border village between the two Koreas, when he crossed the area’s Military Demarcation Line, the U.N. Command wrote in a tweet early Tuesday.

“We believe he is currently in DPRK custody and are working with our KPA counterparts to resolve this incident,” the body said, referring to North Korea by its formal name, the Democratic People’s Republic of Korea, and its army.

The Pentagon official said authorities are not ready to release the man’s identity given they have yet notified his next of kin.

The U.S. State Department did not immediately respond to NPR’s request for comment.

The DMZ divides the two Koreas, approximately around the 38th parallel, and is the de facto international border. It is heavily fortified and mined on both sides.

The two countries stopped fighting in 1953 with an armistice agreement, but are still technically at war.

The U.S. State Department warns U.S. citizens against traveling to North Korea due to “the continuing serious risk of arrest and long-term detention of U.S. nationals,” including the “critical threat of wrongful detention.”

That travel warning was implemented in 2015, after U.S. college student Otto Warmbier was detained by North Korean authorities while touring the area. He was released to the U.S. in a coma in 2017 and died two days later.

This is a developing story and will be updated with more details. Please refresh the page for the latest version.

NPR’s Tom Bowman contributed reporting from Washington D.C. and Se Eun Gong contributed reporting from Seoul.