Iran says 60% enrichment response to Israel's 'nuclear terrorism'
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Tehran starting up advanced centrifuges and producing more highly refined uranium "is a response to your malice," Rouhani said in a message aimed at the Jewish state.
Tehran's announcement of stepped-up enrichment has cast a shadow over talks in Vienna aimed at salvaging the 2015 nuclear deal between Iran and world powers that then US president Donald Trump abandoned almost three years ago.
Iran's regional rival Saudi Arabia also expressed concern and called on Tehran to "avoid escalation".
The Natanz attack unleashed a "dangerous spiral," Iran's Foreign Minister Mohammad Javad Zarif wrote on Twitter.
He warned US President Joe Biden that the situation can only be contained by lifting sanctions Trump imposed on Iran since 2018.
"No alternative. Not much time," he added.
Israel has neither confirmed nor denied involvement but public radio reports in the country said it was a sabotage operation by the Mossad spy agency, citing unnamed intelligence sources.
Iran's envoy to the UN's International Atomic Energy Agency, Kazem Gharibabadi, wrote on Twitter that preparatory steps to allow enrichment to higher purity had started and that "we expect to accumulate the product next week" from centrifuges at Natanz.
The step will bring Iran closer to the 90 percent purity threshold for military use and shorten its potential "breakout time" to build an atomic bomb -- a goal the Islamic republic denies it is seeking.
Iran has also never minced words when it comes to the Jewish state. Supreme leader Ayatollah Ali Khamenei in 2018 reaffirmed Tehran's long-held position that Israel is "a malignant cancerous tumour" that must "be removed and eradicated".
Israel, the only country in the region believed to have nuclear weapons, is strongly opposed to Biden's efforts to revive what it regards as a flawed nuclear agreement between Iran and the UN Security Council's five permanent members plus Germany.
The accord, agreed when Biden was vice-president to Barack Obama, promised Tehran relief from punishing sanctions in return for agreeing to limits on its nuclear programme.
Iran has said it requires the more highly enriched uranium for medical purposes. Gharibabadi said in his tweet that the new material "will improve significantly both the quality and quantity of radiopharmaceutical products".
Robert Kelley, a former IAEA director of inspections, described the leap to 60 percent as "very provocative", in comments to AFP.
Iran had greatly increased the number and performance of its centrifuges, making them "bigger, better, faster," he said.
Kelley also noted, however, that Iran was not making military-grade uranium as "no one in his right mind is trying to make a bomb with 60 percent".