"If the US keeps insisting what does not exist exists and delays the settlement of the nuclear issue, it would have a serious impact on the disablement of nuclear facilities...," a foreign ministry spokesman said in a statement carried by the Korean Central News Agency.
North Korea last year signed a six-nation deal under which it would disable its main atomic plants at Yongbyon and declare all its nuclear programmes and materials by the end of 2007.
The US-supervised disablement has been going ahead, but Washington and Pyongyang cannot agree on the declaration. The North says it submitted the declaration last November. But the United States says Pyongyang has not fully accounted for a suspected uranium enrichment programme and allegations of nuclear proliferation to Syria.
The North denies it ever had an uranium enrichment programme.