North Korea's ambassador to the United Nations, Mr Pak Gil Yon, has refused to deny that his country had nuclear weapons.
Earlier the country, which Washington has placed with Iraq and Iran in an "axis of evil", announced it was pulling out of the nuclear Non-Proliferation Treaty.
The UN nuclear watchdog agency has urged North Korea to reverse its decision.
Asked if the International Atomic Energy Agency (IAEA) would now pass the matter over to the UN Security Council, IAEA spokesman Mark Gwozdecky said: "There's still an opportunity for diplomacy. It's not over until its over".
He also said IAEA chief Mohamed El-Baradei, who meets US Secretary of State Colin Powell today, "strongly urges North Korea to reverse its decision".
Pyongyang also rejected the IAEA's call for North Korea to readmit inspectors and restore United Nations surveillance cameras at the Yongbyon nuclear facilities, which are capable of producing weapons-grade plutonium.
Agencies