VIENNA - The head of the UN atomic watchdog hit out Monday at Iran's lack of cooperation in a probe into its nuclear programme, three weeks after Tehran missed a deadline to provide important information.

"In order to resolve all outstanding issues, it is very important that Iran continues to implement, in a timely manner, all practical measures agreed" to improve transparency, International Atomic Energy Agency chief Yukiya Amano said.

This was despite Iran's "statement of a firm, high-level commitment... and its stated willingness to accelerate the resolution of all outstanding issues," Amano told the IAEA's board of governors, according to the text of his speech.

The IAEA regularly inspects Iran's nuclear facilities, but it also wants Iran to respond to allegations that its programme in the past had "possible military dimensions" -- in other words that it researched how to build a nuclear bomb.

After years of rejecting these claims, progress began to be made last November, with Iran providing the IAEA with explanations on one suspect area and in May promising information on two more.

Iran however failed to do so by a mutually agreed August 25 deadline. Amano said Monday merely that it and Tehran has "begun discussions".

It also failed to propose new measures by September 2 as requested, he said.

Iran's envoy to the IAEA, Reza Najafi, said last week that Iran had already informed the agency that the August 25 deadline would not be met and that further talks would be held in Tehran in late September.

Not answering the IAEA's long-standing questions could harm the chances of a potentially historic deal between Iran and world powers, experts say. (AFP)