Iran's nuclear chief condemned on Sunday what he described as "sabotage" against the Natanz nuclear site, state news agency Irna reported.
The enrichment site was affected by a power disruption only hours after starting new advanced centrifuges, state TV reported.
The incident on Sunday involved the electrical distribution grid at the site and is the latest in a series of problems to befall Iran's most secure nuclear development site.
“The action taken against the Natanz enrichment centre reflects the failure of those who oppose the country’s industrial and political progress to prevent development,” Irna quoted Ali Akbar Salihi as saying.
“The Islamic Republic of Iran, while condemning this despicable action, stresses the need for the international community and the International Atomic Energy Agency to deal with this nuclear terrorism."
Iran, he said, reserved the right to "take action against the perpetrators, commanders and managers" of what occurred at Natanz.
“Fortunately, the incident has not caused any human damage or contamination,” a state TV anchorwoman quoted Behrouz Kamalvandi, a spokesman for Iran’s civilian nuclear programme, as saying.
“The cause of the incident is under investigation.”
A Farsi word state television attributed to Mr Kamalvandi in its report can also be used for "accident".
The Atomic Energy Organisation of Iran, the civilian arm of its nuclear programme, later published a statement using the same wording as the TV report.
On Saturday, Iran announced the installation of a chain of 164 IR-6 centrifuges at the plant. It also announced testing of IR-9 centrifuges said to be able to enrich uranium 50 times faster that Iran's first-generation IR-1 centrifuges.
Under the 2015 nuclear deal, Iran is limited to using only IR-1s for enrichment.
The Natanz plant, previously a target of the Stuxnet computer virus to derail nuclear enrichment, was built underground to withstand enemy air strikes.
It fuelled western fears about Iran's nuclear programme in 2002, when satellite photos showed underground centrifuge housings being built at the site, which is 200 kilometres south of Tehran.
Natanz suffered a mysterious explosion at its advanced centrifuge assembly plant in July that authorities later described as sabotage.
Iran is rebuilding the plant deep inside a nearby mountain.
Israel has been suspected of carrying out an attack there, as well as launching other assaults, as world powers negotiate with Tehran in Vienna over its 2015 nuclear deal.
The US and Iran laid out tough stances at indirect talks in Vienna last week aimed at bringing both back into full compliance with the accord.
Iran also blamed Israel for last year’s killing of a scientist who began the country’s military nuclear programme decades ago.
Israel has not claimed any of the attacks, although in recent weeks Prime Minister Benjamin Netanyahu has repeatedly described Iran as the major threat faced by his country.
On Tuesday, an Iranian cargo ship said to serve as a floating base for Iran's paramilitary Revolutionary Guard forces off the coast of Yemen was struck by an explosion, probably from a limpet mine.
Iran has blamed Israel for the blast. That attack escalated a long-running shadow war in Middle East waterways targeting shipping in the region.
US Defence Secretary Lloyd Austin landed in Israel on Sunday for talks with Mr Netanyahu and Israeli Defence Minister Benny Gantz.
Natanz hosts Iran’s main uranium enrichment plant. In its long underground halls, centrifuges rapidly spin uranium hexafluoride gas to enrich uranium.
Since former US president Donald Trump's withdrawal from the Iran nuclear deal in 2018, Tehran has abandoned all the limits of its uranium stockpile.
It now enriches up to 20 per cent purity, a technical step away from weapons-grade levels of 90 per cent.
Iran maintains its atomic programme is for peaceful purposes. But world powers reached a deal with the country in 2015 to prevent it developing the ability to make a bomb.
The agreement lifted economic sanctions on Iran in exchange for it limiting its programme and allowing inspectors from the International Atomic Energy Agency to keep a close eye on its work.
