Iran is preparing for a possible major expansion of uranium enrichment in a fortified underground facility, a UN nuclear watchdog report showed, underlining Tehran's defiance in the face of Western pressure and the threat of an Israeli attack.

The UN International Atomic Energy Agency (IAEA) report also said "extensive activities" - a reference to suspected sanitisation efforts - at Iran's Parchin military complex would hamper its investigation of possible past nuclear weapons development work there, if inspectors were granted access.

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The number of enrichment centrifuges at Fordo, buried deep inside a mountain to better protect it against any enemy strikes, had more than doubled to 2,140 from 1,064 in May, showed the quarterly report released on Thursday. However, the new machines were not yet operating, it said.

The report further suggested that Iran has effectively shut down a probe of a site suspected of being used for work on nuclear weapons development while doubling the number of machines it could use to make the core of nuclear warheads at an underground bunker safe from airborne attack.

Iran, which denies developing nuclear weapons technology, says it needs this material to fuel a medical research reactor, but it also takes it significantly closer to making potential bomb material.

The report is likely to add to Western alarm about Iran's nuclear ambitions and may further fuel speculation that Israel might launch air strikes against Iranian nuclear sites.

Fordo, where Iran is refining uranium to a level that takes it significantly closer to weapons-grade material, is built to house roughly 3,000 centrifuges - machines that spin at supersonic speed to increase the fissile concentration.

The May report said Iran had installed a total of 1,064 centrifuges, of which 696 were operating, in some six cascades.





Ali Asghar Soltanieh, Iran's envoy to IAEA (Photo: AP)

Iran says it needs this higher-grade uranium for a medical research reactor in Tehran. It is enriching uranium to lower levels at its main such plant in Natanz, where diplomats say it is also installing more centrifuges.

While the newly added centrifuges at Fordo are not yet operating, the expansion reaffirmed Iranian defiance of international demands to suspend enrichment, which can have both civilian and military uses depending on refinement level.





What is Iran hiding in Fordo? (Photo: ISIS website)

"There is reason to be concerned by increased tempo of enrichment, the larger stockpile of enriched uranium and, most importantly, the additional centrifuges installed in the deeply-buried facility at Fordo," said Mark Fitzpatrick of the International Institute of Strategic Studies think-tank.

It may reinforce the belief in Israel that diplomatic and economic pressure is failing to make the Islamic Republic curb its uranium enrichment program.

"We are closely studying the details of the report, but broadly speaking it is not surprising that Iran is continuing to violate its obligations," White House Press Secretary Jay Carney told reporters when asked about the report. "As the report illustrates, we are in a position to closely observe Iran's program," he said.

Carney said the US has made it clear to Iran that they have a limited window of time to stop its atomic work and diplomatic terms offered by the Western world will not remain open "indefinitely."

Iran denies allegations it seeks a nuclear weapons capability and says all its atom work is for peaceful purposes. It has threatened wide-ranging reprisals if attacked.

Iran's supreme leader, Ayatollah Ali Khamenei, on Thursday told heads of state from developing countries at a meting in Tehran that the country has no interest in nuclear weapons but will keep pursuing peaceful nuclear energy.

AP contributed to this report

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