"Significant progress" has been made in a long-stalled probe into allegations that Iran sought to develop nuclear weapons in the past, the UN atomic watchdog head said Monday.

"Significant progress has been achieved," International Atomic Energy Agency chief Yukiya Amano said following a trip this weekend to Iran during which he visited the contentious military base Parchin.

Speaking to reporters at IAEA headquarters in Vienna, Amano added however that "much work remains" before the investigation can be completed by a December 15 deadline.

The IAEA keeps close tabs on Iran's declared nuclear facilities to ensure that no atomic material is diverted by Iran to any covert weapons programme, an aim denied strenuously by Tehran.

Under a landmark deal between Iran and six major powers agreed in July, Iran will dramatically scale down its nuclear activities and the IAEA will be given additional oversight responsibilities.

But the IAEA also wants to probe allegations that at least until 2003, Iran conducted research into making nuclear weapons, including through explosives tests at Parchin.

On July 14 -- the same day as the wider deal with major powers -- Iran and the IAEA agreed a separate "road map" agreement aimed at completing the investigation by December 15.

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