The Natanz site near Tehran was hit by a power outage on Sunday, a day after Iran said it started up advanced uranian enrichment centrifuges in breach of a hobbled 2015 agreement on curbing the country's nuclear ambitions.

On Monday, Tehran labelled the power outage "terrorism" and blamed it on arch-enemy Israel.

The Russian foreign ministry said in a statement that it was closely following the situation surrounding the "serious incident".

"If it is confirmed that someone's malicious actions are behind this incident, then such intent deserves strong condemnation," it said.

The ministry added that it is "alarming how this situation" could affect talks in Vienna on reviving the deal, which are set to resume Wednesday.

The signatories to the accord, known as the Joint Comprehensive Plan of Action (JCPOA), are trying to keep it alive after former US president Donald Trump unilaterally withdrew in 2018 and reimposed sanctions on Iran.

"We hope that what happened will not become a 'gift' to the assorted opponents of the JCPOA and will not undermine the consultations that are gaining momentum... to revive these agreements," the Russian foreign ministry said.

Moscow has pushed for Washington and Tehran to return to the deal, which Israel strongly opposes.