North Korea said Sunday that it has detained yet another U.S. citizen for conducting "hostile acts," raising the number of U.S. citizens known to be detained in the reclusive state to four.

The state-run Korean Central News Agency reported that Kim Hak-song was detained on Saturday with an investigation underway into "his crimes."

The U.S. citizen had been working for Pyongyang University of Science and Technology, the KCNA added.

The detention came after the North announced on Wednesday that Kim Sang-dok, a U.S. citizen who was invited to teach at the same university, was arrested on April 22 for "committing criminal acts of hostility aimed to overturn the DPRK."

DPRK is the acronym of North Korea's official name, the Democratic People's Republic of Korea.

With the latest detention, a total of four U.S. citizens reportedly remain in custody in North Korea. (Yonhap)