SEOUL, South Korea — North Korea has detained a United States citizen, the Swedish Embassy in Pyongyang and a university chancellor said Sunday, raising the number of Americans thought to be held by the secretive nation to three.

The arrest, if confirmed, would further complicate Washington’s relations with the country at a particularly tense moment.

The man, Tony Kim, who also goes by his Korean name, Kim Sang-duk, was detained on Saturday, Park Chan-mo, the chancellor of Pyongyang University of Science and Technology, told The Associated Press.

Mr. Park said Mr. Kim had taught accounting at the university for about a month, and had taught at Yanbian University of Science and Technology in China before coming to Pyongyang. He said Mr. Kim had been detained by officials at Sunan International Airport in Pyongyang as he was trying to leave North Korea.