Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

PYONGYANG, North Korea — A U.S. citizen in his 50s has been detained in North Korea, officials and local media said Sunday.

Pyongyang University of Science Technology confirmed to NBC News that Kim Sang-duk, who also goes by Tony, was detained by North Korean authorities on Saturday at Pyongyang Airport as he was preparing to leave the country.

Kim taught accounting, The Associated Press reported, and he'd been in the country for several weeks, the university said in a statement

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

"We understand that this detention is related to an investigation into matters that are not connected in any way with the work of" the school, the statement said.

The school did not provide additional details.

The Swedish Embassy in Pyongyang said it was aware of a Korean-American citizen being detained recently. "It is this embassy’s understanding that the information that a U.S. citizen has been detained in the DPRK is correct," Martina Aberg, deputy head of mission for the Swedish Embassy in North Korea, said in an email to NBC News.

"We do not comment on individual consular cases that we are working on," Aberg added. The embassy looks after consular affairs for the United States in North Korea because there is no official diplomatic relationship between the two countries.

The detention brings the total number of Americans held by the isolated country to three.

An official at South Korea's National Intelligence Service said it was not aware of the reported arrest.

At least two other Americans are currently detained in North Korea. Last year, Otto Warmbier, then a 21-year-old University of Virginia student from suburban Cincinnati, was sentenced to 15 years of hard labor in prison after he confessed to trying to steal a propaganda banner. Kim Dong Chul, who was born in South Korea but is also believed to have U.S. citizenship, is serving a sentence of 10 years for espionage.

At least one other foreigner, a Canadian pastor, is also being detained in North Korea. Hyeon Soo Lim, a South Korean-born Canadian citizen in his 60s, was convicted and sentenced to life in prison in 2015 on charges of trying to use religion to destroy the North Korean system and helping U.S. and South Korean authorities lure and abduct North Korean citizens.