North Korea says there will be no more bilateral talks with South Korea unless the South's secret nuclear experiments are thoroughly investigated.
A spokesman for the North Korean agency which handles official contacts with the South made the pledge Saturday.
Seoul recently admitted that its scientists had extracted a small amount of plutonium in the early 1980s, and had conducted experiments to enrich uranium in 2000, but says the experiments were unauthorized and purely scientific in nature.
Pyongyang is dismissing those claims, saying the experiments were just "the tip of the iceberg" of the South's nuclear activities.
North Korea has already broken off six-nation talks - which include South Korea and the United States - aimed at persuading Pyongyang to end its nuclear weapons programs.