Iranian foreign ministry spokesman Saeed Khatibzadeh labelled the incident Sunday an Israeli act of "terrorism".

The latest of a string of incidents hitting Iran's nuclear programme came days after talks resumed to salvage the battered 2015 Iranian nuclear deal that former US president Donald Trump abandoned.

His successor Joe Biden wants to revive the accord between Iran and a group of world powers, which places limits on the Islamic republic's nuclear programme in return for relief from biting economic sanctions.

Israel strongly opposes the 2015 Iran nuclear deal and has vowed to stop the Islamic republic from building an atomic bomb -- a goal Tehran has always strongly denied pursuing.

Iran initially reported a power blackout had hit the Natanz site Sunday, a day after it announced it had started up advanced uranium enrichment centrifuges banned under the deal.

Israel did not claim responsibility for the incident, but unsourced media reports in the country attributed it to the Israeli security services carrying out a "cyber operation".

The New York Times, quoting unnamed US and Israeli intelligence officials, also said there had been "an Israeli role" in the attack. It reported that a large explosion had "completely destroyed" the power system which fed the site's "underground centrifuges".

- 'Terrorism' -

Foreign ministry spokesman Khatibzadeh said that "of course the Zionist regime, with this action, tried to take revenge on the people of Iran for their patience and wise attitude regarding the lifting of sanctions".

Khatibzadeh vowed that Iran's response would be to take "revenge on the Zionist regime" when and where Tehran chooses.

The head of Iran's atomic energy organisation, Ali Akbar Salehi, said that "this incident was certainly sabotage", state news agency IRNA reported.

He added that Iranian security services had found the cause of the incident, but no details were reported.

In a separate report by the Fars news agency, Salehi was quoted as saying that "the damaged centrifuges will be replaced with even more powerful" ones.

It was still "too early" to determine the damage caused to several of Iran's first-generation centrifuges, he said.

In a related incident, a spokesman for Iran's nuclear organisation, Behrouz Kamalvandi, suffered an accident Sunday while inspecting the site when he "fell from a few meters and suffered light fractures on his feet and head," IRNA said.

- Avoiding 'trap' -

Tehran has blamed Israel's Mossad spy agency for previous attacks on its nuclear facilities and experts -- including the killing last November of its top nuclear scientist, Mohsen Fakhrizadeh.

Natanz was the site of a previous incident last July, during which a building was damaged, an incident for which some Iranian media also blamed Israel.

Israel and Iran have long fought a shadow war, with Israel often striking Iran-allied forces in war-torn Syria. Since early March, both countries have also accused each other of a number of attacks on each others' ships.

Iran's Foreign Minister Mohammad Javad Zarif said Monday that Tehran would not allow the Natanz attack to affect the Vienna talks. Iran must avoid "falling in the trap" set by Israel, he told a parliamentary meeting.

The European Union said it "rejects any attempts" to undermine the Vienna talks and stressed the "need to clarify the facts" over the incident.

The Russian foreign ministry said it was closely following the situation surrounding the "serious incident" and that "if it is confirmed that someone's malicious actions are behind this incident, then such intent deserves strong condemnation".

The ministry added that it is "alarming how this situation" could affect talks in Vienna, which are set to resume Wednesday.

Germany, a partner to the nuclear accord, also warned that the "development in Natanz" was "not a positive contribution" to the negotiations.

Marc Finaud, head of Arms Proliferation at the Geneva Centre for Security Policy, said the Natanz incident was "not really surprising" and appeared aimed at derailing the Vienna talks.

"This process is typical whenever there are peace negotiations," he said. "There are always spoilers to slow down or to sabotage the process, because in this case, it is not only sabotage of centrifuges, it is sabotage of diplomacy."

amh/mj/fz

THE NEW YORK TIMES COMPANY