"A relevant institution of the DPRK detained American citizen Kim Hak Song on May 6 under a law of the DPRK on suspension of his hostile acts against it", the Korean Central News Agency said, using the abbreviation for the North's official name.
He said that Kim Hak-song became a US citizen in the 2000s and returned to China after about 10 years of living in the United States.
Other Americans being held in North Korea include OH native Otto Warmbier, a University of Virginia student who was arrested in January 2016 while he was on a tour of North Korea, and Kim Dong Chul, who was arrested in October 2015 while in North Korea on business.
The other two Americans already held in North Korea are Otto Warmbier, a 22-year-old student and Kim Dong Chul, a 62-year-old Korean-American missionary. North Korea on Wednesday announced the detention of an accounting instructor at the same university, Kim Sang Dok, for "acts of hostility aimed at overthrowing the country". The Associated Press reports that it is "the only privately funded university in North Korea and is unique for having a large number of foreign staff".
The KCNA said Kim had worked for Pyongyang University of Science and Technology. One is former Virginia man Kim Dong-chul, who had been living in the Chinese city of Yanji, near the border with North Korea, and working in a special economic zone in the North as head of a trade and hotel services company.
A State Department official told CNN the United States is "aware of reports" that an American citizen was detained.
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PUST confirmed Kim's arrest, saying he was detained as he was about to leave the country after a visit of several weeks.
Warmbier was accused of committing a "hostile act" for allegedly trying to steal a political banner and was sentenced in March 2016 to 15 years hard labor.
The New York Times reported the announcement comes on the heels of reports that North Korea is preparing another nuclear weapons test.
Some foreigners have said after their release that their declarations of guilt had been coerced while in North Korean custody.
North Korea on Friday accused the USA and South Korean spy agencies of an unsuccessful assassination attempt on leader Kim Jong Un involving biochemical weapons.