North Korea detained an American professor over the weekend on charges of committing "hostile acts" against the regime, state-run media reported Sunday.
The arrest on Saturday of Kim Hak-song raises the number of U.S. citizens currently held in North Korea to four.
The state-run Korean Central News Agency, or KCNA, said the "relevant authority" is investigating Kim, a professor at the private Pyongyang University of Science and Technology, the New York Times reported. The university said in a statement that Kim was carrying out agricultural development work with the school's agricultural farm.
Kim is the second American professor at the university to be detained by North Korean authorities within the past month.
North Korea confirmed last week it had arrested Kim Sang-dusk, also known by his American name, Tony Kim, on allegations of carrying out "hostile criminal acts with an aim to subvert the country. Tony Kim was working at the Pyongyang University of Science and Technology as an accounting professor.
The State Department has confirmed that it is aware of the reports and would work on the issue through the Swedish Embassy in Pyongyang.
The arrests come amid heightened tensions between the United States and North Korea as leader Kim Jong Un continues to pursue his nuclear and ballistic missile programs despite international pushback.