Inside an Iranian nuclear plant. (Photo: ITN)

Behrouz Kamalvandi, a spokesman for Iran’s Atomic Energy Organization, said uranium enriched to 20% was collected for the first time from advanced IR-6 centrifuges on Saturday. He said Iran had informed the UN nuclear watchdog about the development two weeks ago.

Nuclear talks have been at a standstill since March because Iran and the US have differing views.

Iran has set a number of conditions, including asking the US to lift all sanctions related to this deal, and to remove Iran's Islamic Revolutionary Guard Corps from its terrorist organization list. Washington has rejected Tehran's demands.