North Korea announced Sunday that it detained another American citizen for unspecified hostile acts against the state, according to multiple reports.

The state-controlled news company Korean Central News Agency (KCNA) said the government detained Kim Hak Song on Saturday, according to The Associated Press.

Kim works for the Pyongyang University of Science and Technology.

"A relevant institution is now conducting detailed investigation into [Kim Hak Song’s] crimes," KCNA added.

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Last Wednesday, Pyongyang announced that it had detained Kim Sang Dok, who worked at the same university as an accounting instructor, for "acts of hostility aimed to overturn" the North.

It is unclear if the two cases are connected.

The State Department acknowledged the new detention.

"The security of U.S. citizens is one of the department's highest priorities. When a U.S. citizen is reported to be detained in North Korea, we work with the Swedish embassy in Pyongyang," a State Department official said in a statement to Reuters.

Pyongyang's latest actions come amid rising tensions with Washington over the North's nuclear program and ballistic missile tests. The U.S., South Korea and other states have accused North Korea of detaining foreigners for use as diplomatic bargaining chips.

North Korea is now detaining at least four Americans, including Otto Warmbier, a student at the University of Virginia, who is serving a 15-year prison term with hard labor for allegedly committing acts against the state, and Kim Dong Chul, who is serving 10 years with hard labor for allegedly committing acts of espionage.