TEHRAN — Iran's Foreign Minister Javad Zarif has vowed revenge against Israel after an apparent attack on an Iranian nuclear site caused a blackout at the facility over the weekend.

The incident threatens to undermine recently revived diplomatic efforts between Washington and Tehran to revive the 2015 nuclear deal.

Newly inaugurated centrifuges at Iran's Natanz facility, a centerpiece of the country's contentious nuclear program, appeared to have been badly damaged in Sunday's incident, which Tehran has described as an act of "nuclear terrorism."

Israel's army chief hinted at possible Israeli involvement in the attack in comments on Sunday. Several Israeli media outlets, quoting unnamed intelligence sources, said Mossad, the national intelligence agency, was behind the operation but offered no other details.

The most high-profile condemnation from Tehran came on Monday, according to Iran's state-run IRNA news agency, when Zarif reportedly accused Israel of seeking "revenge" over Iran's efforts to lift US sanctions on the country during last week's indirect negotiations to return to the nuclear deal.

"Our stance will be stronger, and our sides in the negotiations must know that our enriching installations were so far the first generation," Zarif said, according to IRNA. "But from now on, we will fill Natanz with further advanced centrifuges with many more folds of power of enrichment."

The details of the incident at Natanz are murky. Iranian officials said Sunday that there was an act of "sabotage" that led to a blackout at the underground facility in the desert of Isfahan. They also said this happened hours after Iran ceremoniously launched advanced centrifuges at the Natanz plant on Sunday.

The extent of the damage is unclear but Zarif's promise to replace the centrifuges indicates that material losses may have been extensive.

Iran denies there were casualties, but the spokesman for the Atomic Energy Organization of Iran, Behrouz Kamalvandi, was badly injured at the facility, according to state media, falling from a height of seven meters on the same day.

Officials have not linked Kamalvandi's reported injuries to the incident. But on Monday, a video was released on social media showing him on a hospital bed vowing "to resist."

"Our nuclear industry is a time-honored and resilient industry. Our battle will be continued. We will resist," said Kamalvandi in a video address.

This is not the first security issue at Natanz. The facility lost a building when a fire broke out last July, in an incident officials described as an attack on its nuclear program. In 2010, the facility was also the target of the Stuxnet cyberattack, which security experts believe was carried out by Israel and the US.

On Saturday, Iranian President Hassan Rouhani announced new advanced uranium enrichment centrifuges at Natanz, maintaining Iran's official line that its nuclear activities were for "peaceful and civil purposes" but touting the country's nuclear ability as stronger than ever before.

The inauguration of the centrifuges came on the 15th anniversary of Iran's National Nuclear Technology Day. The unveiling was yet a show of defiance by Tehran as it begins new talks over the 2015 Joint Comprehensive Plan of Action, which lifted US sanctions on Iran in exchange for curbs on its uranium enrichment program.

In 2018, then-US President Donald Trump withdrew from the deal, unleashing waves of crippling sanctions on Iran. A year later, Tehran began to gradually withdraw from its commitments to the nuclear deal, resuming parts of its uranium enrichment program.

But US President Joe Biden has vowed to return to the JCPOA. For months, Tehran and Washington have been at loggerheads about who should return to the landmark deal first -- Iran says it won't curb enrichment before the US lifts all sanctions, and the US has accused Iran of intransigence.

However, the last week showed signs of the stalemate thawing. Indirect talks between Washington and Tehran in Vienna, where other parties to the JCPOA shuttled between the two sides, appeared fruitful. Both sides have called the dialogue "productive." — Courtesy CNN