Natanz is Iran’s main uranium-enrichment site and was on the list of targets Donald Trump recently asked for options on attacking but then decided against doing so. The nuclear deal states Iran can only accumulate enriched uranium with first-generation IR-1 machines and that those are the only centrifuges it can operate at its underground plant at Natanz, apparently built to withstand aerial bombardment.
An International Atomic Energy Agency report revealed Tehran had installed a cascade, an interlinked cluster, of advanced IR-2m machines underground at Natanz after relocating them from an above-ground base.
The report said it had not fed uranium hexafluoride (UF6) gas, the feedstock for centrifuges, into that cascade.
Iran has breached many restrictions imposed by the 2015 deal on its atomic activities, including on the purity to which it enriches uranium and its stock of enriched uranium.
The violations came in response to Mr Trump’s withdrawal from the nuclear deal in 2018 and the re-imposition of US sanctions against Tehran that had been lifted under the accord.
Last week’s IAEA report said Iran had also begun installing a cascade of IR-4 centrifuges at the underground plant but not a planned third cascade of IR-6 machines.
It is also operating 5,060 IR-1 machines at the underground plant.
The revelations came after Iran warned a US attack on the Islamic Republic would face a “crushing” response.
Government spokesman Ali Rabiei said: “Any action against the Iranian nation would certainly face a crushing response.”
READ MORE: Donald Trump ‘considered attack on Iran’s nuclear sites’
Mr Trump, with two months left in office, conferred with top advisers about the possibility of attacking the Natanz uranium enrichment plant but was dissuaded by them from that option.
The US President has spent all four years of his regime engaging in an aggressive policy against Iran and slapping economic sanctions on a wide variety of Iranian targets.
In January, he ordered a US drone strike that killed Iranian General Qassem Soleimani at Baghdad’s airport but he has shied away from broader military action.
Israeli Energy Minister Yuval Steinitz said: “If I were the Iranians, I would not feel at ease.
“It is very important that the Iranians know that if, indeed, they suddenly dash toward high levels of enrichment, in the direction of nuclear weaponry, they are liable to encounter the military might of the United States – and also, perhaps, of other countries.”
Iran says its nuclear programme is for peaceful needs.
Mr Rabiei accused Israel of waging “psychological warfare” against Iran.
He said: “I personally don’t foresee that it’s probable that the US would want to cause insecurity in the world and the region.”