The head of the international atomic watchdog raised new concerns about the nuclear drives by Iran and North Korea in his annual report to the UN.
Yukio Amano, director general of the International Atomic Energy Agency (IAEA), told the UN General Assembly both governments must ease global concerns about their actions.
Amano reaffirmed recent IAEA reports that Iran "is not providing the necessary cooperation to enable the agency to conclude that all nuclear material in Iran is in peaceful activities.
"I urge Iran to take steps towards the full implementation of all relevant obligations in order to establish international confidence in the exclusively peaceful nature of its nuclear programme."
The UN Security Council has ordered four rounds of sanctions against Iran over its uranium enrichment. Western nations accuse Iran of seeking a nuclear bomb and have demanded tougher action. The Teheran government denies the charge.
Amano said North Korea's nuclear weapons production "remains a matter of serious concern." IAEA inspectors have not been able to carry out checks in the secretive North since April 2009.
North Korea, which has a plutonium bomb, has since announced that it has built a uranium enrichment plant and a light water reactor which would provide new ways to make a nuclear bomb. Amano called the reports "deeply troubling".
"I continue to urge (North Korea) to fully implement all of the relevant resolutions of the IAEA General Conference and the Security Council," he told the UN assembly.
The UN Security Council has also ordered sanctions against North Korea, which pulled out of six nation talks on its nuclear weapons when it kicked out IAEA inspectors in 2009.
