A Korean American professor has been arrested and detained in North Korea, the Swedish Embassy in the reclusive country confirmed on Sunday.

“We have been informed and can confirm that there has been a detention of a U.S. citizen Saturday morning local,” Martina Aberg, the deputy head of mission for the Swedish Embassy in North Korea, told CNN. The Swedish government takes care of matters related to the U.S. in North Korea, as the latter two countries do not have diplomatic relations.

“He was prevented from getting on the flight out of Pyongyang. We don’t comment further than this.”

Tony Kim, a 58-year-old professor who had been in Pyongyang for a month teaching accounting at Pyongyang University of Science and Technology (PUST), was stopped at the airport as he was trying to leave the country, according to Park Chan-Mo, chancellor of PUST.

Kim is also a former professor of Yanbian University of Science and Technology (YUST), located in Jilin, China.

The reasons for his detainment are unclear.

Park additionally told Reuters news agency that “some officials at PUST told [Park] his arrest was not related to his work at PUST.”

“He had been involved with some other activities outside PUST such as helping an orphanage,” he said.

The school, known to have Christian roots and a large funds base from Christians, also issued a statement saying that “life on campus and the teaching at PUST is continuing as normal.”

With Park’s detainment, the total number of U.S. citizens detained in North Korea is brought to three. A university student named Otto Warmbier who was sentenced to 15 years of hard labor, and a Korean-born U.S. citizen named Kim Dong Chul who was sentenced to 10 years of hard labor, are the other two citizens who are still in custody in North Korea.