The head of Iran's Atomic Energy Organization said on Sunday that a problem with the electrical distribution grid of the Natanz nuclear facility was caused by a "terrorist" act.
According to state TV, the agency's chief Ali Akbar Salehi didn't say who Tehran blames for the alleged cyberattack, which some reports attribute to Israel.
The New York Times quoted an unnamed U.S. official who confirmed an Israeli role in the power outage, but said “details were still very sketchy.”
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Intelligence officials said the alleged operation was carried out by Israeli spy agency Mossad.
Speaking at an event with the Israeli military's top brass also on Sunday, Israel's Prime Minister Benjamin Netanyahu said "The fight against Iran and its proxies... is a massive task. The way things are now doesn't mean they will stay that way later on."
"It's very hard to explain what we've done here in Israel, moving from total helplessness... to a global power," Netanyahu added.
Earlier on Sunday, the spokesman for the country's Atomic Energy Organisation (AEOI) had said that a problem with the electrical distribution grid of the Natanz site had caused an incident, Iranian media reported.
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The spokesman, Behrouz Kamalvandi, said earlier that "the incident caused no casualties or contamination".
He said the international community and the International Atomic Energy Agency (IAEA) needed to deal with what he called nuclear terrorism. He added that Iran reserves the right to take action against the perpetrators, TV reported.
Iran's Press TV reported that the incident at the site occurred on Sunday, a day after Tehran launched new advanced uranium enrichment centrifuges there.
The Natanz facility, which is located in the desert in the central province of Isfahan, is the centerpiece of Iran's uranium enrichment program and monitored by inspectors of the International Atomic Energy Agency, the UN nuclear watchdog.
"The incident caused no casualties or contamination," Iran's Atomic Energy Organization spokesman Behrouz Kamalvandi said earlier on Sunday, adding that "electricity was affected at the Natanz facility."
The cause was being investigated, Kamalvandi told Iran's semi-official Fars news agency, but Iranian lawmaker Malek Shariati-Niasar said in a tweet: "This incident ... is strongly suspected to be sabotage or infiltration."
Iran has blamed Israel for last year’s killing of Mohsen Fakhrizadeh, who was seen by Western intelligence services as the mastermind of a covert Iranian nuclear weapons program.
Tehran has denied seeking to build a nuclear bomb. Israel has neither confirmed nor denied responsibility for the killing.
A spokesman for the UN nuclear watchdog said by email: "We are aware of the media reports. We have no comment at this stage."
In July last year, a fire broke out at the Natanz facility, which the government said was an attempt to sabotage Iran's nuclear program. In 2010, the Stuxnet computer virus, widely believed to have been developed by the United States and Israel, was discovered after it was used to attack Natanz.
Israel has not claimed any of the attacks, though Netanyahu repeatedly has described Iran as the major threat faced by his country in recent weeks.
Meeting with U.S. Defense Secretary Austin on Sunday, Gantz said Israel viewed America as an ally against all threats, including Iran.
“The Tehran of today poses a strategic threat to international security, to the entire Middle East and to the state of Israel,” Gantz said. “And we will work closely with our American allies to ensure that any new agreement with Iran will secure the vital interests of the world, of the United States, prevent a dangerous arms race in our region, and protect the state of Israel.”
The incident at Natanz facility comes amid efforts by Tehran and Washington to revive Iran's 2015 nuclear deal with major powers after former U.S. President Donald Trump abandoned it three years ago. Trump reimposed sanctions that had been lifted on the Islamic Republic, and brought in many more.
In reaction to the U.S. sanctions, Iran has gradually breached many restrictions imposed by the accord. The two nations laid out tough stances at indirect talks in Vienna last week on how to bring both back into full compliance with the accord.
President Hassan Rohani reiterated Iran's commitment to nuclear non-proliferation on Saturday while overseeing the launch of advanced centrifuges at the Natanz plant to mark the country's National Nuclear Technology Day.
Yaniv Kubovich contributed to this report.