Iran on Monday blamed Israel for a sabotage attack on its underground Natanz nuclear facility that damaged the centrifuges it uses to enrich uranium there, warning that it would take revenge for the assault.

The comments by Foreign Ministry spokesman Saeed Khatibzadeh represent the first official accusation levelled against Israel for the incident on Sunday that cut power across the facility.

Israel has not directly claimed responsibility for the attack. However, suspicion fell immediately on it as Israeli media widely reported that a devastating cyberattack orchestrated by Israel caused the blackout.

If Israel was responsible, it would further heighten 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 with US Defense Secretary Lloyd Austin, has vowed to do everything in his power to stop the nuclear deal.

Details remained scarce about what happened early on Sunday at the facility. The event was initially described as a blackout caused by the electrical grid feeding its above-ground workshops and underground enrichment halls.

“The answer for Natanz is to take revenge against Israel,” Khatibzadeh said. “Israel will receive its answer through its own path.” He did not elaborate.

Khatibzadeh acknowledged that IR-1 centrifuges, the first-generation workhorse of Iran’s uranium enrichment, had been damaged in the attack, but did not elaborate. State television has yet to show images from the facility.

A former chief of Iran’s paramilitary Revolutionary Guard said the attack had also set off a fire at the site and called for improvements in security at Natanz. In a tweet, Gen. Mohsen Rezaei said that a second fire at Natanz in a year signalled “the seriousness of the infiltration phenomenon.”

Iranian Foreign Minister Mohammad Javad Zarif separately warned that Natanz would be reconstructed with more advanced machines, something that could imperil ongoing talks in Vienna with world powers about saving Tehran’s tattered atomic accord.

“The Zionists wanted to take revenge against the Iranian people for their success on the path of lifting sanctions,” Iran’s state-run IRNA news agency quoted Zairf as saying. “But we do not allow (it) and we will take revenge for this action against the Zionists.”

The IAEA, the United Nations body that monitors Tehran’s atomic program, earlier said it was aware of media reports about the incident at Natanz and had spoken with Iranian officials about it. The agency did not elaborate.

Natanz has been targeted by sabotage in the past. The Stuxnet computer virus, discovered in 2010 and widely believed to be a joint US-Israeli creation, once disrupted and destroyed Iranian centrifuges at Natanz during an earlier period of Western fears about Tehran’s programme.

In July, Natanz suffered a mysterious explosion at its advanced centrifuge assembly plant that authorities later described as sabotage. Iran is now 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.

Media reports

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 the 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.

Netanyahu, on late Sunday, 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,” 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, Netanyahu has repeatedly described Iran as the major threat to his country as he struggles to hold onto power after multiple elections and while facing corruption charges.