Iran's Natanz uranium enrichment site.

On Sunday, the Natanz site near Tehran was hit by a power outage.

EU spokesman Peter Stano said the incident could have been an act of sabotage, but insisted that there has been no official attribution of responsibility. He stressed the need to gather the facts as quickly as possible, but said the EU rejects any attempt to undermine or weaken diplomatic efforts to revive the nuclear agreement.

Russia's foreign ministry said Monday that it hopes the power outage at the Natanz uranium plant, which Tehran denounced as an attack by Israel, will not undermine the talks.

The incident occurred as negotiators in Vienna were seeking to re-admit the United States to the 2015 pact aimed at curbing Iran's nuclear ambitions. Former US president Donald Trump withdrew the US from the deal in 2018.