The Iranian foreign minister has said his country will "take revenge" for an attack on an underground nuclear site, for which it has blamed Israel.
Iranian officials said the Natanz uranium enrichment plant was the target of "nuclear terrorism" on Sunday, after initially reporting a power failure.
New advanced centrifuges to enrich uranium had just been activated there.
Israel has not commented, but public radio cited intelligence sources as saying it was a Mossad cyber operation.
They said it had caused more extensive damage than Iran had reported.
US intelligence officials told the New York Times that a large explosion had completely destroyed the independent internal power system that supplied the centrifuges inside the underground facility. They estimated it could take at least nine months to resume enrichment there.
Iran's Nour News agency, which is affiliated to the Supreme National Security Council, cited an intelligence ministry source as saying the "main perpetrator" had been identified and an operation was under way to arrest them.
Israel has recently stepped up its warnings about its arch-foe's nuclear programme amid efforts to revive a 2015 nuclear deal that was abandoned by former US President Donald Trump.
His successor, Joe Biden, has said he wants to return to the landmark accord. But Iran and the five other world powers still party to it - China, France, Germany, Russia and the UK - need to find a way for him to lift US sanctions and for Iran to return to the agreed limits on its nuclear programme.
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.
The European Union said it still needed to clarify the facts about the Natanz incident, but that it rejected "any attempts to undermine or weaken diplomatic efforts on the nuclear agreement".
US Defence Secretary Lloyd Austin, who is visiting Israel, said he was aware of the reports about Natanz and that the Biden administration's diplomatic efforts to re-engage with Iran diplomatically would continue.
Iran nuclear crisis: The basics
- World powers don't trust Iran: Some countries believe Iran wants nuclear power because it wants to build a nuclear bomb - it denies this.
- So a deal was struck: In 2015, Iran and six other countries reached a major agreement. Iran would stop some nuclear work in return for an end to harsh penalties, or sanctions, hurting its economy.
- What is the problem now? Iran re-started banned nuclear work after former US President Donald Trump pulled out of the deal and re-imposed sanctions on Iran. Even though new leader Joe Biden wants to rejoin, both sides say the other must make the first move.
"The Zionists want to take revenge because of our progress in the way to lift sanctions," Iranian Foreign Minister Mohammad Javad Zarif was quoted by state media as saying on Monday.
"They have publicly said that they will not allow this. But we will take our revenge from the Zionists."
Iran does not recognise Israel's right to exist and often refers to it as the "Zionist state".
Foreign ministry spokesman Saeed Khatibzadeh later told a news conference in the capital, Tehran, that Israel was "of course" behind the attack on Natanz.
"This incident, fortunately, did not cause any damage to human lives or the environment. However, it could have been a catastrophe. This is a crime against humanity and carrying out such actions is in line with the essence of the Zionist regime," he said.
Mr Khatibzadeh said only the least efficient "IR-1" centrifuges were damaged in the incident, and that they would be replaced with advanced ones.
Israeli Prime Minister Benjamin Netanyahu did not mention the incident at a later joint news conference with the US defence secretary.
But he stated: "My policy... is clear: I will never allow Iran to obtain the nuclear capability to carry out its genocidal goal of eliminating Israel. And Israel will continue to defend itself against Iran's aggression and terrorism."
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