Israel has attacked Iran, three people familiar with the matter said, as Iranian state media said early on Friday that its forces had destroyed drones, days after Iran launched a retaliatory drone strike on Israel, according to Reuters.

One source told Reuters the U.S. was not involved but was notified by Israel before the attack.

Iran’s Fars news agency reported three explosions were heard near an army base in the central city of Isfahan. An Iranian official told Reuters there was no missile attack and the explosions were the result of the activation of Iran’s air defense systems.

Iranian state TV said that shortly after midnight “three drones were observed in the sky over Isfahan. The air defense system became active and destroyed these drones in the sky.”

The broadcaster later said the situation in Isfahan was normal and no ground explosions had occurred.

The Israeli military had no comment on the reports.

Israel had said it would retaliate, opens new tab against Iran’s weekend attack, which involved hundreds of drones, opens new tab and missiles, in response to a suspected Israeli strike on its embassy compound in Syria. Most of the Iranian drones and missiles were downed before reaching Israeli territory.

Iranian President Ebrahim Raisi had warned Israel before Friday’s strike that Tehran would deliver a “severe response” to any attack on its territory.

Iran told the United Nations Security Council on Thursday that Israel “must be compelled to stop any further military adventurism against our interests” as the U.N. secretary-general warned that the Middle East was in a “moment of maximum peril.”