North Korea is boosting its arsenal of nuclear weapons, the communist state's Vice-Foreign Minister, Kim Gye-gwan, has told the US ABC News network.
Mr Kim took part in negotiations over the nuclear programme
He said North Korea had enough atomic bombs to protect itself against attack by the US and was building more.
He refused to say whether North Korean missiles could reach the US.
US President George Bush has meanwhile said Pyongyang must show it is ready to give up its nuclear weapons programme in a "serious and substantive" way.
The BBC's Seoul correspondent, Charles Scanlon, says Mr Kim's statement reveals how deeply North Korea and the US disagree over its weapons ambitions.
Six-nation negotiations aimed at getting North Korea to give up its weapons programme have been stalled for over a year.
On Wednesday, the Chinese envoy to the UN said Pyongyang might "soon" return to the negotiating table, following talks between US and North Korean officials on Monday.
Mr Kim told ABC News that North Korea had "enough nuclear bombs to defend against a US attack".
Asked whether North Korea had the technology to attach nuclear warheads to its long-distance missiles, he responded: "I want you to know that our scientists have the knowledge, comparable to other scientists around the world."
President Bush has meanwhile told the US Fox News network North Korea must show it is sincere about giving up its weapons programme.
He said the US had no immediate intention to refer North Korea to the UN.
US officials have publicly vilified the North Korean system and hinted at coercive measures if it does not scrap its nuclear weapons programme.
But they have also made conciliatory gestures, recognising North Korea as a sovereign state and saying they have no intention to attack.
For its part, North Korea claimed earlier this year that it was pushing ahead with its development of nuclear weapons, but it now says it is prepared to return to the six-party talks.
Analysts believe the North has been raising the stakes to try to get the best possible deal, without trying to provoke all-out confrontation.