Iran is currently operating about 4,000 uranium enrichment centrifuges and it is installing several thousand more, the state news agency IRNA quoted the deputy foreign minister as saying yesterday.
"There are nearly 4,000 centrifuges working in the Natanz enrichment facility... another 3,000 centrifuges are being installed," IRNA quoted Alireza Sheikh Attar as saying in an interview with state television.
In July, President Mahmoud Ahmadinejad said Iran had up to 6,000 centrifuges for uranium enrichment, the process at the heart of Western fears that Tehran is secretly trying to build nuclear weapons.
The International Atomic Energy Agency, which has been probing Iran's nuclear activities, said in a May report that Tehran was operating 3,500 centrifuges in Natanz in central Iran.
Iran is under three sets of UN Security Council sanctions over its refusal to halt enrichment and risks further sanctions for failing to give a clear response to an incentives package offered by six world powers in return for halting the sensitive work.
World powers offered to start pre-negotiations with Iran during which Tehran would add no more uranium-enriching centrifuges and in return face no further sanctions.
Iran denies seeking nuclear weapons, insisting that its programme is designed to provide energy for its growing population when the leading Opec member's reserves of fossil fuels run out.
Permanent Security Council members -- Britain, China, France, Russia and the United States -- plus Germany made Iran an offer, which included trade incentives and help with a civilian nuclear programme in return for suspending enrichment.
The United States, which has been pushing for tougher sanctions, has never ruled out a military option over the nuclear standoff.