North Korea on Wednesday confirmed the detention of another American citizen for alleged acts of hostility aimed at overthrowing the country.

Kim Sang Dok, an accounting instructor at Pyongyang University of Science and Technology, was “intercepted” at Pyongyang International Airport on April 22, according to the Korean Central News Agency. It said he was being detained while authorities conduct a detailed investigation into his alleged crime.

The school’s chancellor Park Chan-mo and the Swedish Embassy in Pyongyang earlier gave the information about Kim’s detention but couldn’t provide the reason for his arrest. The school’s report used a different spelling of Kim’s name, Kim Sang-duk. Kim’s English name is Tony Kim.

He is now the third American being detained in North Korea. The other U.S. detainees are Otto Warmbier, serving a 15-year prison term with hard labor for alleged anti-state acts, and Kim Dong Chul, serving a 10-year term with hard labor for alleged espionage.

Analysts say North Korea often attempts to use foreign detainees to wrest outside concessions, which in the past have sometimes involved high-profile American missions sent to secure the release of detainees. Animosity between Pyongyang and Washington has spiked in recent weeks amid a game of brinkmanship between North Korean leader Kim Jong Un and U.S. President Donald Trump.

Park said Kim, who is 58, was detained as he was trying to leave the country from Pyongyang’s international airport. A university spokesman said he was trying to leave with his wife on a flight to China. Park said he was informed that the detention had “nothing to do” with Kim’s work at the university but did not know further details.

The U.S. State Department said last month that it was aware of the report about a U.S. citizen being detained, but declined further comment “due to privacy considerations.”

Kim previously taught Korean at the Yanbian University of Science and Technology in Yanji, China, not far from the North Korea border, according to the school’s Communist Party Committee secretary.

The Pyongyang University of Science and Technology is the only privately funded university in North Korea. It held its first classes in 2010. It is unique in the North for its large number of foreign staff.

(AP)