North Korea broke its silence on the late April detention of U.S. citizen Kim Sang-duk, also known as Tony Kim, in a report on Wednesday in which state media accused Kim of “committing criminal acts of hostility”.

In the report published by the Korean Central News Agency (KCNA), Kim’s behavior was alleged to have “aimed to overturn the DPRK”, though no details were given about the specifics of his actions.

Kim, who was a professor at the Yanbian University of Science and Technology (YUST) in Yanji, China, and was a regular visitor to North Korea to teach at the  Pyongyang University of Science and