"I regret that we are still not in a position to achieve full clarity regarding the absence of undeclared nuclear material and activities in Iran," the head of the International Atomic Energy Agency (IAEA) told the UN General Assembly.
He urged Tehran to "implement all the transparency measures required to build confidence in the exclusively peaceful nature of its nuclear program at an early date."
"This will be good for Iran, good for the Middle East region and good for the world," he added.
He stressed he was confident arrangements could be made to enable the IAEA "to clarify the remaining issues while ensuring Iran's legitimate right to protect the confidentiality of sensitive information and activities is respected."
In his own address to the General Assembly, Iran's UN Ambassador Mohammad Khazaee reiterated that the UN Security Council's demand that the Islamic Republic suspend its uranium enrichment program was "illegal."
"The Iranian nation will never accept illegal demands," he added.
Enrichment is at the heart of Western fears that Iran could be seeking nuclear weapons as it can be diverted to make the fissile material for an atomic bomb as well as fuel for nuclear power plants.
The Security Council has already slapped three rounds of sanctions on Tehran which has refused to suspend uranium enrichment insisting its nuclear program is strictly peaceful and solely aimed at generating electricity.
Six major powers — Britain, China, France, Germany, Russia and the United States — have put forward the possibility of a package of technological, economic and political incentives if it suspends uranium enrichment.
