North Korea has said that news of recent nuclear experiments in the South has made it even more determined not to abandon its own weapons programme.
Seoul says only miniscule amounts of nuclear material were produced
South Korea has admitted experimenting with plutonium and uranium and has been chided by the United States.
The North accused the US of backing the research and said international talks on its nuclear plans were in question.
Delegations of Chinese and British officials are currently holding talks in the North's capital, Pyongyang.
The north said Washington had adopted double standards on nuclear technology.
"It has transferred nuclear technology to its 'allies' and connived at their nuclear weapons-related activities and possession of nuclear weapons," a spokesman for the North Korean foreign ministry said on Saturday.
"But it has worked hard to stamp out nuclear activities for a peaceful purpose after faking up 'misinformation' about [North Korea] on account of its ideology
The row centres on recent revelations in the South:
- Seoul admitted extracting a small amount of plutonium - a key ingredient in nuclear bombs - in secret research conducted in the early 1980s
South Korean scientists produced 0.2 of a gram of uranium in 2000 through scientists who did not have government approval
Unconfirmed reports are also emerging of other undisclosed nuclear tests
The BBC's Charles Scanlon reports from Seoul that the North appears determined to use the revelations about the South to maximum effect.
"It is self-evident that [North Korea] can never abandon its nuclear programme under such a situation..." the North's foreign ministry said.
"We cannot but link these cases to the issue of resuming the six-party talks."
The talks on the North's programme - which involve both Koreas, the US, China, Russia and Japan - were stalling already, our correspondent says.
But now the North has ammunition to question the South's true intentions and to justify its own well-advanced atomic bomb programme,
A high-level delegation from China, the North's main ally, arrived in Pyongyang on Friday for talks which observers see as a last-ditch attempt to save the six-party negotiations.
The delegation's leader, Li Changchun, is expected to meet North Korea's leader, Kim Jong-Il.
UK Foreign Office minister Bill Rammell has also arrived in the Communist state in a bid to start a new dialogue over its nuclear weapons programme as well as its human rights record.