The U.N. nuclear chief said Monday that Iran is blocking his watchdog agency from verifying whether the nation has any ambitions for nuclear weaponry.

"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," Mohamed ElBaradei, the head of the International Atomic Energy Agency, told the U.N. General Assembly.

He urged Iran to do more to ensure "transparency," but emphasized the Vienna-based IAEA "does not in any way seek to pry into Iran''s conventional or missile-related military activities."

Iranian Ambassador Mohammad Khazaee countered that the U.N. Security Council''s demand that his nation suspend uranium enrichment is "illegal."

Iran''s nuclear program, he said, is only for peaceful purposes and designed to produce nuclear energy and the nation "will never accept illegal demands."

Khazaee also said that the five permanent members of the Security Council — the U.S., Britain, China, Russia and France — plus Germany never responded to Tehran''s proposal that they negotiate without preconditions. The six powers have offered economic and political incentives if Iran suspends its enrichment work.