A nuclear facility in Iran was hit by "sabotage" a day after it unveiled new uranium enrichment equipment, the country's top nuclear official says.
Ali Akbar Salehi did not say who was to blame for the "terrorist act", which caused a power failure at the Natanz complex south of Tehran on Sunday.
Israeli public media, however, cited intelligence sources who said it was the result of an Israeli cyber-attack.
Israel has not commented on the incident directly.
But in recent days it has ramped up its warnings about Iran's nuclear programme.
The latest incident comes as diplomatic efforts to revive a 2015 nuclear deal - abandoned by the US under the Trump administration in 2018 - have resumed.
On Saturday, Iran's President Hassan Rouhani inaugurated new centrifuges at the Natanz site in a ceremony that was broadcast live on television. Centrifuges are devices needed to produce enriched uranium, which can be used to make reactor fuel as well as nuclear weapons.
It represented another breach of the country's undertakings in the 2015 deal, which only permits Iran to produce and store limited quantities of enriched uranium to be used to produce fuel for commercial power plants.