North Korea said on Sunday that it had detained another American citizen for “hostile acts” against the country. According to North Korea’s official news agency KCNA, Kim Hak Song, who was working at the Pyongyang University of Science and Technology, was detained on Saturday. If confirmed, he is the fourth American currently being held by the DPRK. Kim Sang Dok, an American who was a visiting professor at the university, was detained late last month under similar circumstances. The detentions come as tensions between the U.S. and North Korea are mounting over the north’s acceleration of its nuclear weapons program.