An electrical problem has been reported at Iran's Natanz nuclear site, a day after Tehran launched new advanced centrifuges that enrich uranium more quickly.
It was the latest incident to strike one of Tehran's most secure sites amid negotiations over the tattered atomic accord with world powers.
"The incident caused no casualties or pollution," Iranian Atomic Energy Organization spokesman Behrouz Kamalvandi said, adding that "electricity was affected at the Natanz facility."
Last year, a fire broke out at the Natanz nuclear facility that the government said was an attempt to sabotage its nuclear program.
The underground Natanz site is key to Iran's uranium enrichment program and monitored by inspectors of the International Atomic Energy Agency (IAEA), the UN nuclear watchdog.
Israel, Iran's regional archenemy, is suspected of carrying out an attack there, as well as launching other assaults.
Iran also blamed Israel for the killing of a scientist who began the country's military nuclear program decades earlier. Israel has not claimed any of the attacks, though Prime Minister Benjamin Netanyahu has repeatedly described Iran as the major threat faced by his country in recent weeks.
The incident at Natanz comes amid efforts to revive the international 2015 nuclear deal between Iran and major powers that former U.S. President Donald Trump withdrew the United States from three years ago. Trump reimposed sanctions that were lifted on the Islamic republic, and brought in many more.
In reaction, Iran breached many restrictions imposed by the accord. Tehran has abandoned all the limits of its uranium stockpile. It now enriches up to 20 percent purity, a technical step away from weapons-grade levels of 90 percent.
Earlier this week, talks began in Vienna aimed at bringing the United States and Iran back into full compliance with the deal.
On April 10, Iran announced it had launched a chain of 164 IR-6 centrifuges at Natanz, injecting them with the uranium gas and beginning their rapid spinning.
Officials also began testing the IR-9 centrifuge, which they say will enrich uranium 50 times faster than Iran's first-generation centrifuges, the IR-1. The nuclear deal limited Iran to using only IR-1s for enrichment.
Iran maintains its nuclear program is solely for peaceful purposes, but fears about Tehran having the ability to make a bomb saw world powers reach the deal with the Islamic republic in 2015.
The deal lifted economic sanctions on Iran in exchange for it limiting its program and allowing inspectors from the IAEA to keep a close watch on its work.