North Korea on Friday denied reports that it had mistreated the former U.S. detainee Otto Warmbier and described his sudden death as a "mystery", in the country's first public statement since the announcement of the 22-year-old's death on Wednesday.

In a statement by a DPRK Foreign Ministry spokesman carried by the Korean Central News Agency (KCNA), the North Korean representative claimed the country has been the victim of a "smear campaign" by the U.S.  as part of a "frantic effort" to impose "heinous sanctions".