Iran's top nuclear official, Ali Akbar Salehi called an attack on the Natanz nuclear facility a "despicable" act that was meant to sabotage nuclear talks between Tehran and the signatories of its 2015 nuclear agreement currently underway in Vienna.

A day after injecting uranium gas into new advanced centrifuge machines, the spokesman of Iran's Atomic Energy Organization (AEOI) Behrouz Kamalvandi reported early Sunday "an accident in the electricity grid" of the underground Natanz enrichment facility. 

“The accident caused no casualties or pollution,” Kamalvandi said Sunday morning without specifying the time of the incident. The incident has affected the electricity distribution grid of the facility, he added. He did not provide any more details about the impact of the incident on operations at Natanz.

Later, The jerusalem Post reported that what happened in Natanz "was not an accident" but most probably a cyberattack by Israel, similar to past attacks in 2010 by the Stuxnet virus and in July 2020. The incident happened on Iran's National Nuclear Day, adding to suspicions that the incident was an act of sabotage. Israeli sources said that the attack was much more serious than what was reported by Iran.

Salehi also stated that "The action against the Natanz enrichment site shows the defeat of those who are opposed to Iran's nuclear and political accomplishments...and successful negotiations for removing oppressive sanction."

The incident comes as talks in Vienna between Iran and world powers focused on ways to revive the 2015 nuclear agreement, JCPOA. Israel and Gulf Arab states have voiced their deep concern over the Biden Administration attempts to return to the deal that Trump abandoned and lift sanctions imposed since 2018.

Iran announced on Staurday that it has repaired a part of the Natanz facility that was damaged by a mysterious explosion last July, that authorities attributed to "sabotage". On Saturday in an interview with the state-run TV (IRIB), Iran's nuclear chief Ali-Akbar Salehi said "the enemy" was responsible for destroying the centrifuge assembly-line of Natanz with an explosion. "We did not give up and built a new location inside a mountain near Natanz. We are working to relocate our sensitive facilities to underground locations in the mountains," he said and added that the locations required for housing sensitive facilities are expected to be ready next year. 

On Saturday, during ceremonies to mark Iran's National Nuclear Energy Day, Iran unveiled "133 new nuclear achievements" in several facilities in Tehran, Markazi, Isfahan, Alborz and Qom provinces which according to the state-controlled English language channel Press TV included quantum, enrichment, heavy water and deuterium compounds, radiopharmaceuticals and lasers. President Hassan Rouhani who ordered the launch of a cascade of 164 advanced IR-6 centrifuges and two test cascades of IR-5 and IR-6S advanced centrifuges on Saturday said that Iran continues to be committed to its pledge to the Non-Proliferation Treaty (NPT).

A series of mysterious explosions and fires occurred at Iran's military and nuclear facilities including Parchin and Khojir military zones and the Natanz enrichment facility in late June and July 2020, including the  centrifuge manufacturing plant of Natanz. "The financial damages [to the plant at the Natanz facility] were significant," AEOI Spokesman Behrouz Kamalvandi said on July 6.

Hours after the July incident at Natanz, the official government news agency (IRNA) said there was a possibility of Israel's involvement in the incident. Besides explosions in Iran's military and nuclear facilities, Israel has also been blamed for assassination of several of Iran's nuclear scientist including Mohsen Fakhrizadeh on November 26, 2020 outside Tehran.  

The former US President Donald Trump unilaterally withdrew from the JCPOA in 2018 and reimposed draconian sanctions on Iran. Iran retaliated the withdrawal of the United States and the reimposition of sanctions with several major breaches of its own commitments under the deal including enrichment to the purity level of 20%. Iran says it now has 60 kg of 20% enriched uranium.