Rising tensions:An engineer at the Natanz plant, in a screen grab from a videoconference held in Tehran on Saturday.AFP-  

Iran’s underground Natanz nuclear facility lost power on Sunday just hours after starting up new advanced centrifuges capable of enriching uranium faster, the latest incident to strike the site amid negotiations over the tattered atomic accord with world powers.

Iran described a blackout at its Natanz atomic facility an act of “nuclear terrorism,” raising regional tensions.

Ali Akbar Salehi, the head of the Atomic Energy Organization of Iran, stopped short of directly blaming anyone for the incident. Details remained few about what happened early on Sunday morning at the facility, which initially was described as a blackout caused by the electrical grid feeding the site.

Multiple Israeli media outlets reported on Sunday that an Israeli cyberattack caused the blackout in Natanz. Public broadcaster Kan said the Mossad was behind the attack. Channel 12 TV cited “experts” as estimating the attack shut down entire sections of the facility. While the reports offered no sourcing for their information, Israeli media maintains a close relationship with the country’s intelligence agencies.

If Israel caused the blackout, it further heightens tensions between the two nations, already engaged in a shadow conflict across the wider West Asia.

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“To thwart the goals of this terrorist movement, the Islamic Republic of Iran will continue to seriously improve nuclear technology on the one hand and to lift oppressive sanctions on the other hand,” Mr. Salehi said, according to state TV.

He added: “While condemning this desperate move, the Islamic Republic of Iran emphasises the need for a confrontation by the international bodies and the (International Atomic Energy Agency) against this nuclear terrorism.”

Sunday’s developments also complicates efforts by the U.S., Israel’s main security partner, to re-enter the atomic accord aimed at limiting Tehran’s nuclear programme. Israeli Prime Minister Benjamin Netanyahu, who on Sunday met with U.S. Defense Secretary Lloyd Austin, has vowed to do everything in his power to stop the nuclear deal.

“It’s hard for me to believe it’s a coincidence,” Yoel Guzansky, a senior fellow at Tel Aviv’s Institute for National Security Studies, said of Sunday’s blackout. “If it’s not a coincidence, and that’s a big if, someone is trying to send a message that ‘we can limit Iran’s advance and we have red lines.’” It also sends a message that Iran’s most sensitive nuclear site is “penetrable,” he added.

Israel typically doesn’t discuss operations carried out by its Mossad intelligence agency or specialised military units. In recent weeks, Mr. Netanyahu has repeatedly described Iran as the major threat to his country.

‘Sabotage, infiltration’

Malek Shariati Niasar, a Tehran-based lawmaker who serves as spokesman for the Iranian Parliament’s energy committee, wrote on Twitter that the incident was “very suspicious,” raising concerns about possible “sabotage and infiltration.” He said lawmakers were pursuing details of the incident as well.

Natanz was built largely underground to withstand enemy airstrikes. It became a flashpoint for Western fears about Iran’s nuclear plan in 2002, when satellite photos showed Iran building its underground centrifuges facility at the site.