Chad Baker/Jason Reed/Ryan McVay/Photodisc/Thinkstock(PYONGYANG, North Korea) -- U.S. citizens being held in North Korean prisons will be subjected to wartime laws, a Pyongyang diplomat told ABC News in an exclusive interview.



The basis for a wartime designation of prisoners such as Otto Warmbier and Kim Dong Chul, two Americans being held there, is Pyongyang's claim that U.N. sanctions against North Korea amount to a "declaration of war,” the official, Han Son Ryol, the country’s diplomat dealing with U.S. affairs, said.



The United Nations Security Council ordered economic sanctions against North Korea in 2013 in response to nuclear tests conducted by the country. The resolution was negotiated between the United States and China, which is widely regarded as North Korea’s strongest ally in the region.



The wartime declaration comes on the heels of a report by South Korea's Yonhap News Agency that claimed North Korea launched a ballistic missile into Japan's exclusive economic zone for the first time Wednesday, an incident that has raised tensions in the region.



The United States and Japan have since acknowledged the reported launch, which Prime Minister Shinzo Abe called an "unforgivable act of aggression."



It is unclear what the wartime designation would mean for Warmbier or Kim.



Warmbier, a 21-year-old University of Virginia student who had been traveling to the country as part of a backpacking tour, was detained by North Korean authorities in January for trying to steal a propaganda poster from the Yanggakdo International Hotel, where he was staying in Pyongyang with other Westerners.



Warmbier was sentenced in March to 15 years of hard labor, after an hour-long trial



"I was used and manipulated," he said during the trial, weeping. "Please save my life."



Former New Mexico Gov. Bill Richardson, who has also served as the U.S. ambassador to the United Nations and energy secretary in the Clinton administration, was enlisted by Warmbier's family to help negotiate for the release of their son on humanitarian grounds.



Richardson called the 15-year sentence "crazy" in an interview with ABC News in March.



Kim Dong Chul, a South Korea-born businessman and naturalized U.S. citizen, had been living in China with his wife at the time of his arrest in North Korea on charges of espionage. He was sentenced to 10 years in prison with hard labor after a brief trial in Pyongyang in April.



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