North Korea on Saturday dashed the South's hope of quickly resuming bilateral talks between the two old Cold War enemies, declaring there is no hope for progress unless South Korea's nuclear experiments are fully investigated.
North Korea has already broken off slow-moving six-country talks aimed at ending its nuclear weapons programmes in return for compensation.
It has also boycotted a series of scheduled talks with the South since July, when Seoul successfully airlifted more than 460 North Korean refugees from Vietnam, angering the North.
"It will be impossible to expect any development of the inter-Korean relations unless the truth about South Korea's secret nuclear experiments is probed," the North's KCNA news agency quoted a spokesman for the Committee for the Peaceful Reunification of the Fatherland as saying.
The committee is North Korea's official channel of dealings with the South, the counterpart to Seoul's Unification Ministry.
The statement refers to recently disclosed experiments conducted in the South by government scientists to enrich uranium in 2000 and to separate plutonium in 1982, neither of which the South Korean government said was authorised or known.
South Korea's Foreign Minister Ban Ki-moon told Reuters last month that there had never been and would not be a government programme to develop nuclear weapons.
But North Korea said the experiments were "all but a tip of the iceberg of the serious nuclear development activities that the South Korean authorities have so far conducted in a premeditated manner."
"The clandestine nuclear development pursued for over 20 years helped South Korea acquire basic criteria for nuclear armament such as extraction of nuclear substance, production of nukes, access to means for nuclear delivery and preparations for a nuclear war and put all this under a perfect system."
North Korea has said it was impossible to return to the six-party talks - hosted three times by Pyongyang's ally China and attended by South Korea the United States, Japan and Russia - because Washington was seeking to destroy it by disarming it and then launching a pre-emptive nuclear attack.
The United States denies the claim and said North Korea would benefit from dismantling its nuclear programmes, including a uranium enrichment programme.