DUBAI, United Arab Emirates — Iran on Sunday described a blackout at its underground Natanz atomic facility an act of “nuclear terrorism,” raising regional tensions as world powers and Tehran continue to negotiate over its tattered nuclear deal.

While there was no immediate claim of responsibility, suspicion fell immediately on Israel, where its media nearly uniformly reported a devastating cyberattack orchestrated by the country caused the blackout.

If Israel was responsible, it further heightens tensions between the two nations, already engaged in a shadow conflict across the wider Middle East. Israeli Prime Minister Benjamin Netanyahu, who met Sunday with U.S. Defense Secretary Lloyd Austin, has vowed to do everything in his power to stop the nuclear deal.

Details remained few about what happened early Sunday morning at the facility, which initially was described as a blackout caused by the electrical grid feeding its above-ground workshops and underground enrichment halls.

Ali Akbar Salehi, the American-educated head of the Atomic Energy Organization of Iran, who once served as the country’s foreign minister, offered what appeared to be the harshest comments of his long career, which included the assassination of nuclear scientists a decade ago. Iran blames Israel for those killings as well.

He pledged to “seriously improve” his nation’s nuclear technology while working to lift international sanctions.

Salehi’s comments to state TV did not explain what happened at the facility, but his words suggested a serious disruption.

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

The IAEA, the United Nations’ body that monitors Tehran’s atomic program, earlier said it was aware of media reports about the incident at Natanz and had spoken with Iranian officials about it. The agency did not elaborate.