Iran is now operating 492 new centrifuges at the Natanz uranium enrichment plant, the agency quoted an informed source as saying, in defiance of UN calls to freeze the process which the West fears could be used to make the bomb.

President Mahmoud Ahmadinejad announced on Tuesday that Iran was working to install 6,000 more centrifuges at an underground hall in the plant but gave not figures on how many of the new centrifuges were operational.

The IRNA report was the first time an official source has given numbers to go with the progress.

According to the UN nuclear watchdog, Iran has already installed around 3,000 of the centrifuges at the uranium enrichment plant in central Iran and the 492 new machines are part of a second series of installations.

"Three cascades of 164 centrifuges from the second series of 3,000 centrifuges are operational in Natanz," the source, who was not named, told the agency.

The source added that the new centrifuges were of the original P1 type and not the faster models that Iran has been testing at an above-ground research facility at the plant.

This new generation of machines are Iran's version of the more efficient P2 centrifuges -- the IR-2 -- which officials say can enrich uranium with five times the output capacity of the standard P1s.

Ahmadinejad's announcement on Tuesday came as Iran marked its "national day of nuclear technology" on the second anniversary of its first production of uranium sufficiently enriched to make atomic fuel.

It provoked an angry international reaction with Western countries warning Tehran faces further sanctions if it continues to expand its nuclear drive.

The West fears Iran could use enriched uranium to make a nuclear weapon, and Tehran's refusal to suspend the process has been punished with three sets of UN Security Council sanctions and US pressure on its banking system.

But Iran insists that its nuclear programme is entirely peaceful and solely aimed at generating energy for a growing population whose supply of fossil fuels will eventually run out.

Some diplomats have said that Iran has experienced difficulties in utilising its existing centrifuges to full capacity.

But the deputy head of Iran's Atomic Energy Organisation, Mohammad Saeedi, told IRNA on Friday that "there are no technical problems regarding the development of centrifuges."

Despite the international alarm about the expansion of Iran's nuclear drive, US Secretary of State Condoleezza Rice has expressed scepticism about the latest nuclear announcements from Tehran.

"I can't substantiate the claims. There are always multiple claims coming out of Iran about progress on this, progress on that. I don't think the underlying situation has changed," Rice said on Tuesday.

related report
Iran envoy set for talks with UN nuclear chief The head of the Iranian Atomic Energy Organisation is to travel to Vienna on Monday for talks with the head of the UN nuclear watchdog, Mohamed ElBaradei, the official IRNA news agency said.

"Gholamreza Aghazadeh will travel to Vienna on Monday for talks with Mohamed ElBaradei," it reported on Saturday.

The visit comes after President Mahmoud Ahmadinejad sparked an angry international reaction on Tuesday with the announcement that Iran was working to install 6,000 more centrifuges at its Natanz uranium enrichment plant.

Western governments warned Tehran that it faced further sanctions if it continues to expand its nuclear programme, which they fear is cover for a drive to develop an atomic weapon.

But Iran insists that its nuclear programme is entirely peaceful and aimed solely at generating energy for a growing population whose supply of fossil fuels will eventually run out.

Iran says that it will discuss its nuclear programme only with the UN watchdog -- the International Atomic Energy Agency.

It insists there is no basis for involvement by the UN Security Council, which has already imposed three sets of sanctions over Iran's failure to heed repeated ultimatums to suspend uranium enrichment.

related report
Iran says no 'technical problems' in nuclear programme Iran denied Friday that it faced any "technical problems" in expanding its controversial nuclear programme, which the West fears could be diverted towards weapons development.

"There are no technical problems regarding the development of centrifuges," deputy head of Iran's Atomic Energy Organisation, Mohammad Saeedi told the state IRNA news agency.

On Tuesday Iran announced it had started to install thousands of new centrifuges to enrich uranium at its main nuclear plant in Natanz, in defiance of international demands that it halt enrichment.

But diplomats say Iran has experienced difficulties in utilising its existing centrifuges to full capacity.

Iran's ambassador to the International Atomic Energy Agency, Ali Asghar Soltanieh, has said it was "natural in this kind of industry that there are ups and downs once in a while."

Uranium enrichment lies at the core of the standoff over Iran's nuclear programme, as the process, which makes nuclear fuel, could be used to make atom bombs.

As a signatory to the nuclear Non-Proliferation Treaty, Iran insists it has a right to enrichment to make nuclear fuel to meet growing energy needs of its population and vehemently denies allegations of seeking a bomb.

Tehran's refusal to suspend enrichment has been punished with three sets of UN Security Council sanctions and US pressure on its banking system.

But Tehran has rejected the UN Security Council resolutions as "political and illegal" and vowed to press on with its nuclear programme in the face of pressure.