If Israel was responsible, it further heightens tensions between the two nations, already engaged in a shadow conflict across the wider Middle East.
Israeli Prime Minister Benjamin Netanyahu, who met on Sunday (local time) with US Defence Secretary Lloyd Austin, has vowed to do everything in his power to stop the nuclear deal.
Details remained few about what happened early on Sunday morning at the facility, which initially was described as a blackout caused by the electrical grid feeding its above-ground workshops and underground enrichment halls.
Iran’s Atomic Energy Organisation condemned the incident, calling it a “terrorist action,” according to the Iranian telegram channel of the Revolution Guard Corps, or IRGC.
Akbar Salehi, chief of the organisation, said, “Today’s attack demonstrates that the enemies of Iran’s progress and advancement in nuclear science, as well as nuclear negotiations, are in desperation committing terrorist actions against the nuclear technology at Natanz (nuclear facility),” reported IRGC, a branch of the Iranian Armed Forces.
Mr Salehi also said, “Iran reserves the right to respond against the perpetrators, and those who committed the terrorist action,” IRGC reported.
Earlier on Sunday, Iranian officials confirmed an “incident” at Natanz, a day after the government said it was launching more than 150 new uranium enrichment centrifuges at the underground facility.
“Fortunately, the incident did not cause any human injuries or leaks,” said Behrouz Kamalvand, a spokesman for the Atomic Energy Organisation.
“The causes of the accident are under investigation and further information will be announced later.”
During the 15th anniversary of Iran’s National Nuclear Technology Day on Saturday, Iranian President Hassan Rouhani announced new uranium enrichment centrifuges at the plant, stating that while Iran’s nuclear activities are for “peaceful and civil purposes,” the country’s nuclear capability was also stronger than at any time before.
“Today, a chain of 164 IR-6 centrifuges was launched,” Mr Rouhani said, according to state-run Press TV.
“It can provide us with products 10 times more than the former chain.”
The Natanz nuclear plant lost a building when a fire broke out last July.
The Iranian government said at the time that it was an attack on its nuclear program.
It was also the target of the Stuxnet cyberattack in 2010, which security experts believe was carried out by Israel and the US.
Natanz suffered a mysterious explosion at its advanced centrifuge assembly plant in July last year that authorities later described as sabotage.
Iran now is rebuilding that facility deep inside a nearby mountain.
Iran also blamed Israel for the November killing of a scientist who began the country’s military nuclear program decades earlier.
Multiple Israeli media outlets reported on Sunday that an Israeli cyberattack caused the blackout in Natanz.
Public broadcaster Kan said the Mossad was behind the attack.
Channel 12 TV cited “experts” as estimating the attack shut down entire sections of the facility.
While the reports offered no sourcing for their information, Israeli media maintains a close relationship with the country’s military and intelligence agencies.
“It’s hard for me to believe it’s a coincidence,” Yoel Guzansky, a senior fellow at Tel Aviv’s Institute for National Security Studies, said of Sunday’s blackout.
“If it’s not a coincidence, and that’s a big if, someone is trying to send a message that ‘we can limit Iran’s advance and we have red lines.'”
It also sends a message that Iran’s most sensitive nuclear site is “penetrable,” he added.
Mr Netanyahu later on Sunday night toasted his security chiefs, with the head of the Mossad, Yossi Cohen, at his side on the eve of his country’s Independence Day.
“It is very difficult to explain what we have accomplished,” Mr Netanyahu said of Israel’s history, saying the country had been transformed from a position of weakness into a “world power.”
Israel typically doesn’t discuss operations carried out by its Mossad intelligence agency or specialised military units.
In recent weeks, Mr Netanyahu repeatedly has described Iran as the major threat to his country as he struggles to hold onto power after multiple elections and while facing corruption charges.
Speaking at the event on Sunday night, Mr Netanyahu urged his security chiefs to “continue in this direction, and to continue to keep the sword of David in your hands,” using an expression referring to Jewish strength.
With CNN, Associated Press