Mr. Kim was detained at the airport in the capital, Pyongyang, on April 22 while he was trying to leave the country. His arrest raised the number of Americans thought to be held by the secretive nation to three.

Image Mr. Kim had taught accounting at a university in China before traveling to Pyongyang, where he taught at a sister school.

Mr. Kim’s detention comes at a particularly tense moment in relations between the United States and North Korea. As the North has conducted banned tests of ballistic missiles in recent weeks, the United States dispatched an aircraft carrier strike group to waters off the Korean Peninsula as a show of force.

Mr. Kim had taught accounting at Yanbian University of Science and Technology in China before traveling to Pyongyang, where he taught for about a month at a sister school, the Pyongyang University of Science and Technology, according to Park Chan-mo, the university’s chancellor.

The South Korean news agency Yonhap said Mr. Kim was also engaged in humanitarian work in the North, helping orphanages in the country’s northeast.

The North has been accused of holding Americans on what many see as dubious charges in order to use them as diplomatic leverage. At least two other Americans are known to be held in the country.