Iran on Sunday confirmed an "incident" at a nuclear plant in Natanz, a day after the government said it was launching more than 150 new uranium enrichment centrifuges at the underground facility.
In local news agency reports, Iranian officials suggested the facility may have come under attack, speculating the plant may have been targeted as the country discusses a revival of the Iran nuclear deal with its Western signatories.
Former US President Donald Trump withdrew the United States from the agreement.
Behrouz Kamalvand, a spokesman for Iran's Atomic Energy Organization, acknowledged the incident had affected the electricity grid of the facility, the semi-official news agency Fars reported Sunday.
"Fortunately, the incident did not cause any human injuries or leaks," Kamalvand said. "The causes of the accident are under investigation and further information will be announced later."
Malek Shariati Niaser, a member of Iran's Parliament, added: "The blackout in Natanz on the anniversary of National Nuclear Day is suspicious and may be due to sabotage while Iran is trying to convince the western countries to lift the sanctions," the semi-official news website Entekhab.ir reported.
A spokesman for the International Atomic Energy Agency told CNN by email on Sunday the agency was aware of the media reports.
"We have no comment at this stage," he said.
During the 15th anniversary of Iran's National Nuclear Technology Day 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," Rouhani said Saturday, 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.
Talks wrapped up in Vienna this week between Iran and other signatories of the Iran nuclear deal. US officials were also in Vienna and met with representatives from global powers who are still party to the deal. They did not meet with Iranian officials directly.
Trump began imposing new sanctions on Iran as he withdrew the country from the deal. Iranian officials have maintained that the US must lift all Trump-era sanctions and return to the nuclear deal before it again complies with the agreement.