North Korea on Sunday said it detained another American citizen over unspecified hostile acts against the country.

North Korea’s official Korean Central News Agency said Kim Hak Song, an employee of the Pyongyang University of Science and Technology, was detained Saturday.

It follows another recent detention. 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.” Park Chan-mo, the chancellor of the Pyongyang University of Science and Technology, had said last month that Kim was detained by officials as he was trying to leave the country from Pyongyang’s international airport.

The KCNA didn’t say whether the two cases are connected.