Iran has installed hundreds more centrifuges that could enable it to enrich uranium faster since May, a UN atomic watchdog report showed Wednesday, as long-stalled talks were due to resume.

"Iran has continued to install IR-2m centrifuges in one of the units" at the Natanz site, the International Atomic Energy Agency said in its quarterly report, seen by AFP.

The Islamic republic now has 1,008 high-tech IR-2M centrifuges, up from 698 cited in the IAEA's last report in May.

These were " under vacuum", however, the report said.

The IR-2 centrifuges are of particular concern as they would allow Tehran to enrich uranium at a faster rate, allowing it to obtain the amount of fissile material needed for a nuclear bomb more quickly, if it wished to go down that path.

Western countries suspect Iran is trying to develop an atomic bomb but Tehran insists its nuclear programme is solely for peaceful purposes.

Earlier Wednesday, the IAEA said that talks with Iran over its controversial nuclear programme would resume on September 27.

The talks were held up by presidential elections in Iran in June.