The United Nations Command on Tuesday said an American national had crossed the border from South Korea into North Korea.

The command, charged with ensuring security on the Korean Peninsula, said the man crossed the border into the North without authorization and is now in North Korean custody.

Unnamed US officials later told several news agencies that the man is a US solider.

What we know so far

The US citizen had been on a tour to the Joint Security Area (JSA), the border village in the demilitarized zone that separates the two Koreas and where soldiers from both sides stand guard. North Korea and South Korea are officially still at war.

"We believe he is currently in [North Korean] custody and are working with our KPA counterparts to resolve this incident," the command added, referring to North Korea's People's Army.

The JSA, also known as Panmunjom, is a popular tourist destination. It attracts hundreds of visitors every day who tour the area on the South Korean side.

Donald Trump met North Korean leader Kim Jong Un at the Panmunjom Truce Village in 2019 and even stepped across the demarcation line onto North Korean soil.

The incident on Tuesday comes as relations between the two Koreas are at a low, with diplomatic efforts between the two sides stalled.

Cases of US or South Korean citizens defecting to North Korea are rare. However, more than 30,000 North Koreans have fled to South Korea to avoid political oppression and economic hardship since the de facto end of the 1950-53 Korean War.

A US State Department travel advisory tells US nationals not to enter North Korea "due to the continuing serious risk of arrest and long-term detention of US nationals."

The advice was made more emphatic than previously after US college student Otto Warmbier was detained by North Korean authorities while visiting the country in 2015. Warmbier died in 2017, days after being released from prison and returning to the United States in a coma.