Iran has begun installing advanced centrifuges at its main uranium enrichment plant, the UN nuclear watchdog said yesterday, a defiant step that will worry Western powers ahead of a resumption of talks with Tehran next week.

In a confidential report, the International Atomic Energy Agency (IAEA) said 180 so-called IR-2m centrifuges and empty centrifuge casings had been put in place at the facility near the town of Natanz in central Iran. They were not yet operating.

If launched successfully, such machines could enable Iran to speed up significantly its accumulation of material that the West fears could be used to devise a nuclear weapon.

Iran says it is refining uranium only for peaceful energy purposes.

The installation of new-generation centrifuges would be “yet another provocative step,” US State Department spokeswoman Victoria Nuland said in Washington.

White House spokesman Jay Carney warned Iran that it would face further pressure and isolation if it failed to address international concerns about its nuclear programme in the February 26 talks with world powers in the Kazakh city of Almaty.

Britain’s Foreign Office said the IAEA’s finding was of “serious concern”. Israeli Prime Minister Benjamin Netanyahu’s office said the report “proves that Iran continues to advance swiftly towards the red line” that he laid down last year.

Netanyahu, who has strongly hinted at possible military action if sanctions and diplomacy fail to halt Iran’s nuclear drive, told the United Nations in September Iran must not be allowed to amass enough higher-enriched uranium to make even a single warhead.

Iran denies Western accusations that it is seeking to develop a capability to make atomic bombs. Tehran says it is Israel’s assumed nuclear arsenal that threatens peace.

Iran’s envoy to the IAEA, Ali Asghar Soltanieh, said the UN agency’s report showed “no evidence of diversion of material and nuclear activities towards military purposes.”