The South Korean military says it has detained a U.S. citizen who was apparently trying to swim across a river into North Korea.
Seoul's defense ministry said the man was detained late Tuesday by South Korean marines guarding the Han River near the Demilitarized Zone.
The Yonhap news agency reported the man, who appeared to be in his 30s, was found lying on the shore, apparently exhausted from swimming.
The report said the man told officials he wanted to meet with North Korean leader Kim Jong Un.
U.S. officials have not commented on the incident, which would be a rare instance of an American crossing into the North illegally from South Korea.
South Korean soldiers last year shot and killed a South Korean man who tried to cross another river into North Korea.
North Korea is currently holding at least three other U.S. citizens.
On Sunday, a Pyongyang court gave a sentence of six years of hard labor to Matthew Miller, who in April ripped up his visa at immigration and demanded asylum in the North. He was convicted of committing "hostile acts" against the government.
A trial is also expected soon for Jeffrey Fowle, who entered the North as a tourist and was arrested in May for leaving a Bible at a provincial club.
A third U.S. citizen, Korean-American missionary Kenneth Bae, is serving out a 15-year sentence for what Pyongyang called "hostile acts" intended to overthrow the government.
The three detainees recently were allowed to speak to U.S. media outlets. They appealed to the U.S. government to help free them.
Planned trips by a U.S. diplomat to secure Bae's freedom have been canceled by Pyongyang. Those visits were scheduled to take place before Miller and Fowle were arrested.
In the past, North Korea has released detained Americans after high-profile visits by former U.S. Presidents Bill Clinton and Jimmy Carter.