North Korea claimed on Thursday it has the sovereign right to “ruthlessly punish” American citizens it delayed and accused of crimes against its government system.

Pyongyang said it is “pure ignorance” of U.S. media calling its action as a bargaining ploy.

The North’s KCNA news agency reported that the crimes of the withheld Americans will be made public soon.

Two American citizens working for a private university in the North’s capital are under detention in the last month.

Kim Hak-Song was the fourth American held captive by the Korean government on May 7 for espionage and crimes against the state.

Kim Dong-chul, who is a naturalized American, born in South Korea, has been held for the longest period ever by the Korean authorities. He is a 60-year-old businessman who once lived in Fairfax Virginia.

58-year-old American, Tony Kim, also named Kim Sang-duk, who was temporarily accountant lecturer at Pyongyang University of Science and Technology, was held at the airport while about boarding a flight to China on April 22.