"Anyone who challenges our dignity and social system and agrees to go ahead with the establishment of the office will be ruthlessly punished," the North's Committee for the Peaceful Reunification of Korea said in a statement.
The committee handles issues related to South Korea. South Korean president Park Geun-hye and others from international human rights organisations would "pay the price", the statement, carried by the official KCNA news agency, said. The planned office was a "hideous politically-motivated provocation", and an "anti-North Korean plot-breeding organisation," led by South Korea and the United States, it added.
North Korea "categorically and totally" rejected the accusations set out in the report, saying they were based on material faked by hostile forces backed by the United States, the European Union and Japan.
North Korea called Michael Kirby, the Australian judge who led the investigation and held hearings in South Korea, Japan, Britain and the United States, a "disgusting old lecher with a 40-odd-year-long career of homosexuality".
North Korea is under UN, US and other national sanctions due to repeated nuclear and ballistic missile tests since 2006 in defiance of international demands to stop.