“We believe he is currently in [North Korean] custody and are working with our KPA counterparts to resolve this incident,” Taylor said, referring to the Democratic People’s Republic of Korea and its armed forces.

The American, whom officials did not identify by name, was visiting the Joint Security Area that separates North and South Korea while on an “orientation tour,” Taylor said.

The soldier had been punished for misconduct while serving in South Korea and was being sent home to the United States, according to a U.S. official. But he did not get on his scheduled flight after U.S. military personnel took him to the airport, the official said, who spoke on the condition of anonymity because of the matter’s sensitivity.

The United States is trying to determine his whereabouts and condition, the official added.

The Joint Security Area is an 800-meter-wide bubble within the demilitarized zone between North and South Korea where diplomatic discussions can take place. The border area, one of the most fortified in the world, is overseen by the United Nations.

According to the United Nations Command, Korean nationals and foreign tourists are able to visit more than a dozen “Education and Orientation Program sites” within the demilitarized zone, where visitors can learn about the Korean War and the subsequent armistice agreement. It was not immediately clear whether the detained U.S. national was visiting one of those sites. Public tours to the area were suspended for most of the coronavirus pandemic.

The Joint Security Area in the inter-Korean border village of Panmunjom is a popular civilian tourist destination and a rare opportunity for visitors to witness what is technically both North Korean and South Korean territory.

Guards from both countries stand face to face near the iconic, identical light-blue buildings on each side of the line.

The 1950-1953 Korean War ended in an armistice, rather than a peace treaty, and both Koreas technically remain at war.

Tuesday’s incident comes amid a years-long diplomatic stalemate between the United States and North Korea, since the collapse of nuclear negotiations at a summit in 2019.

The United States and South Korea, meanwhile, have drawn closer to each other in the past year. On Tuesday, a U.S. nuclear-armed ballistic missile submarine visited South Korea for the first time since the 1980s in a show of unity in the face of Pyongyang’s growing ballistic missile threats.

U.S. and South Korean officials are meeting this week in Seoul, where the two countries are holding “nuclear consultation” talks designed to assure South Koreans of America’s commitment to defending its democratic ally in case of an attack from the North.

The State Department in 2017 imposed a travel ban on U.S. nationals traveling to North Korea after the death of Otto Warmbier, an American student who traveled to Pyongyang with a tourist group in 2015 and was arrested and detained on charges of stealing a propaganda poster. He died days after being flown home in a coma.

The U.S. government is unable to provide emergency services to its citizens in the country, the State Department notes in its travel advisory on North Korea, because no diplomatic or consular relations exist between Washington and Pyongyang.

The U.S. State Department did not immediately respond to a request for more information early Tuesday. The South Korean Joint Chiefs of Staff said it did not have immediate information available on the incident.

Shane Harris contributed to this report.