An electrical power problem caused an incident at Iran's Natanz underground nuclear facility on Sunday, Iranian Press TV reported, a day after Tehran launched new advanced uranium enrichment centrifuges at the site.
"The incident caused no casualties or contamination," Iran's Atomic Energy Organization spokesman Behrouz Kamalvandi said, adding that "electricity was affected at the Natanz facility", which is located in the desert in the central province of Isfahan.
The underground Natanz site is the centrepiece of Iran's uranium enrichment programme and monitored by inspectors of the International Atomic Energy Agency, the U.N. nuclear watchdog.
"The cause of this incident is under investigation," Kamalvandi told Iran's semi-official Fars news agency.
In July last year, a fire broke out at the Natanz facility, which the government said was an attempt to sabotage Iran's nuclear programme. In 2010, the Stuxnet computer virus, widely believed to have been developed by the United States and Israel, was discovered after it was used to attack Natanz.
Tehran and Washington have been trying to revive Iran's 2015 nuclear deal with major powers after former U.S. President Donald Trump abandoned it three years ago. Trump reimposed sanctions that had been lifted on the Islamic Republic, and brought in many more.
In reaction to the U.S. sanctions, Iran breached many restrictions imposed by the accord. The two nations laid out tough stances at indirect talks in Vienna last week on how to bring both back into full compliance with the accord.
President Hassan Rouhani reiterated Iran's commitment to nuclear non-proliferation on Saturday while overseeing the launch of advanced centrifuges at the Natanz plant to mark the country's National Nuclear Technology Day.