The White House said Monday that the United States had nothing to do with what Iran says was a sabotage attack on its Natanz uranium enrichment plant.
"The US was not involved in any manner," Press Secretary Jen Psaki told reporters. "We have nothing to add on speculation about the causes or the impacts."
Iran accused its arch-enemy Israel of being behind the attack, and vowed it would take "revenge" and ramp up its nuclear activities.
The Atomic Energy Organization of Iran (AEOI) said a "small explosion" had hit the plant's electricity distribution center Sunday in what the foreign ministry labelled an Israeli act of "terrorism."
Iran initially reported a power blackout had hit the Natanz site, a day after it announced it had started up advanced uranium enrichment centrifuges banned under the battered 2015 Iranian nuclear deal.
Israel did not claim responsibility for the incident, but unsourced media reports in the country attributed it to a "cyber operation" by the Israeli security services.
The New York Times, quoting unnamed US and Israeli intelligence officials, also said there had been "an Israeli role" in the attack.
The incident at Natanz came days after talks resumed in Vienna to salvage the multinational nuclear deal, which 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 program in return for relief from punishing economic sanctions.
Psaki said Monday that the incident would not derail the talks, in which Washington is taking part indirectly.
"Our focus of course is on the diplomatic path forward. We've not been given any indication that attendance at the discussions that will proceed on Wednesday has changed," she said.