"To be frank, for some time now we have been going around in circles," Yukiya Amano told a closed-door quarterly meeting of the International Atomic Energy Agency's board of governors.
"This is not the right way to address issues of such great importance to the international community, including Iran," he said, according to the text of his speech in Vienna.
"We need to achieve concrete results without further delay to restore international confidence in the peaceful nature of Iran's nuclear activities."
Iran says the IAEA's findings are based on faulty intelligence from foreign spy agencies such as the CIA and Israel's Mossad -- intelligence it complains it has not even been allowed to see.
The sites that the agency wants to visit include the Parchin military base near Tehran, where it suspects Iran built a large explosives containment vessel to conduct experiments that the IAEA says would be "strong indicators of possible nuclear weapon development".
Parallel negotiations between Iran and six world powers -- the US, China, Russia, Britain, France and Germany -- are also stalled following the latest gathering in Almaty, Kazakhstan in early April.
This diplomatic track, on hold until after Iran's June 14 elections, is focused more on Iran's current activities which, as the IAEA's latest quarterly report circulated on May 22 made clear, Iran has continued to expand in spite of UN Security Council resolutions calling for a suspension.
