(CNN) North Korea detained a US citizen for unknown reasons as he was planning to fly out of Pyongyang International Airport on Saturday morning. Kim Sang Duk, also known as Tony Kim, was teaching at Pyongyang University of Science and Technology, a statement from the school said.
The detention comes amid a buildup of tension on the Korean Peninsula, with a North Korean newspaper saying Sunday that Pyongyang was ready to sink a US aircraft carrier conducting drills in the region. Kim is the third US citizen in North Korean custody.
The school said he was detained by authorities at the airport “after several weeks of service, teaching at PUST.”
“We understand this detention is related to an investigation into matters not connected in any way with the work of PUST,” the school said.
“We cannot comment on anything that Mr. Kim may be alleged to have done that is not related to his teaching work on the PUST campus.”
The statement said “life on campus and the teaching at PUST is continuing as normal” for the spring semester.
The detained American is a professor, the South Korea’s Yonhap News Agency reported.