Iran has begun dismantling parts of its nuclear programme, as agreed under July's landmark deal with major powers, a UN atomic watchdog report showed Wednesday.

Iran "has started removing centrifuges and related infrastructure" at both the Natanz and Fordo enrichment facilities, said the restricted International Atomic Energy Agency quarterly report, seen by AFP.

Under the July 14 deal that ended a potentially dangerous decade-long standoff, Iran undertook to dramatically scale back its nuclear programme.

These steps, coupled with increased UN oversight, are aimed at making it much more difficult for Iran to develop nuclear weapons, an aim it has always denied.

They include slashing by two-thirds the number of centrifuges, machines which can "enrich" or purify uranium to make it suitable for peaceful uses but also for a nuclear weapon.

In addition, Iran pledged to change the design of a new reactor at Arak in order to reduce sharply the amount of plutonium produced, the alternative to uranium for a bomb.

In return, the six major powers -- the United States, Russia, China, Britain, France and Germany -- have agreed to lift sanctions imposed on the Islamic republic.

The accord was formally adopted by all parties on October 18 and "Implementation Day", when it enters into force, is expected in the coming weeks or months.

- Some way to go -

The IAEA report showed though that despite taking out around a quarter of its roughly 19,000 installed centrifuges, Iran still has some way to go before all its commitments are met.

So far 4,500 centrifuges have been removed at Natanz and Fordo, the IAEA report showed, meaning it still has to take out roughly another 10,000 to get to the target of 5,000.

In addition, no preparatory work has taken place at Arak, the IAEA's report showed, and Iran's stock of enriched uranium gas grew to around 8.3 tonnes (18,300 pounds), an increase of 460 kilos.

Under the July deal, this stock -- which could in theory be purified to weapons-grade -- has to be slashed to just 300 kilos.

Separately to verifying that Iran downscales its activities, the Vienna-based IAEA is also probing allegations that at least until 2003, Iran conducted research into developing nuclear weapons.

The watchdog is aiming to compile a final report on these so-called "possible military dimensions" of Iran's activities by December 15, although diplomats say it could be released before that.

Iran says that the allegations are false and based on bogus intelligence provided to a gullible and partial IAEA by the likes of the US Central Intelligence Agency (CIA) and Israel's Mossad.