"Natanz incident said to cause huge damage, set back Iran’s program by 9 months"
Thousands of machines used to refine nuclear material were destroyed or damaged in an attack at a key site on Sunday, an Iranian official has said.
Alireza Zakani, head of the Iranian parliament's Research Centre, said the incident had "eliminated" Iran's ability to carry out the process.
The attack took place in a facility up to 50m (165ft) underground, another official said.
Iran has blamed Israel for what it called an act of "nuclear terrorism".
Israel has neither confirmed nor denied involvement, but Israel public radio cited intelligence sources as saying it was a Mossad cyber-operation.
Iran says it will replace the affected centrifuges - machines used to refine, or enrich, the chemical element uranium for use in nuclear energy or potentially nuclear bombs - with more advanced ones.
It also announced on Wednesday that it would greatly increase the quality of enrichment - from 20% to 60% purity. Enriching to either level is prohibited under the terms of the 2015 nuclear deal, and while 60% is significantly closer to the 90% required for a nuclear weapon, it is still some way off.
Meanwhile, Israeli and Arab media reports say an Israeli-owned vessel has been damaged in an attack off the coast of the United Arab Emirates.
Unnamed officials quoted by Israel's Channel 12 TV blamed Iran for the strike on the Hyperion Ray. If confirmed, it would be the latest in a series of alleged tit-for-tat attacks on Israeli and Iranian vessels.
Iran had initially acknowledged that centrifuges were damaged, but without elaborating.
However, speaking on the state-run Ofoq TV channel, Mr. Zakani said the damage was extensive.
"Is it normal that today they reach a pit of our electricity system and take actions so that several thousand centrifuges are damaged and destroyed in one instant?" he asked.
"Should not we be sensitive over the incident that happened [on Sunday], eliminating the main part of our enrichment capacities?"
Iran, which insists it does not want nuclear weapons, has retaliated against the sanctions reinstated by the Trump administration by rolling back key commitments under the deal.
US and Iranian officials are holding indirect talks in the Austrian capital, Vienna, to try to break the impasse, with European officials acting as intermediaries.