Iran has played down a drone attack on a munitions centre in Isfahan, calling it a minor incident, but some analysts said the strike was a significant blow to Tehran.
Three drones struck a “military workshop” in the city on Saturday night, Iran's Defence Ministry said, claiming it shot down the unmanned aerial vehicles.
One of the drones caused “minor damage” to the workshop's roof, it said.
It offered no other details on the attack, which occurred as a huge fire broke out at an oil refinery in north-western Iran.
The cause of the blaze is still under investigation, officials have said.
Israel carried out a drone strike on a defence compound in Isfahan, the Wall Street Journal reported, citing unidentified US officials and sources.
“This cowardly act was carried out today as part of the efforts made by enemies of the Iranian nation in recent months to make the Islamic republic insecure,” Foreign Minister Hossein Amirabdollahian told a press conference with his visiting Qatari counterpart, Sheikh Mohammed bin Abdulrahman.
“Such measures cannot affect the will and intention of our specialists for peaceful nuclear developments,” AFP quoted him as saying.
State news outlet Irna hit out at other media for “fearmongering” following the incidents.
The Pentagon said no US military forces had conducted operations inside Iran.
“We continue to monitor the situation, but have nothing further to provide,” the Pentagon's press office told The National.
The attack comes as US Secretary of State Antony Blinken begins a Middle East tour amid soaring regional tension and heightened violence in Jerusalem and the occupied West Bank.
He is expected to discuss the Iranian threat with senior Israeli officials, who have yet to comment on the Saturday attack.
Iran's Foreign Ministry spokesman Nasser Kanaani hit out at Israel on Sunday, saying US support would “not help the regime's survival”.
While Iran said the attack would not stop Tehran from “progressing”, intelligence officials said it was far more destructive that Iran had reported, The Jerusalem Post reported.
Regional outlets reported that the US carried out the strike with a “second country”. American sources denied Israel had participated in the attack.
The strike would mark the first assault on Iran since Israeli Prime Minister Benjamin Netanyahu returned to office in Israel, accompanied by a hardline government that has not only vowed to entrench Israel's occupation but also to clamp down on Iran and its growing nuclear activity.
Israeli officials have so far declined to comment on the strike and rarely acknowledge action in Iran, where the country is thought to have launched several attacks on nuclear sites in recent years.
Israel is suspected of attacking sites such as the Natanz nuclear plant, where Iran is now reportedly increasing its stockpile of enriched uranium.
Tension is also running high with Azerbaijan after a gunman killed one and wounded another outside its embassy in Tehran on Friday, an attack denounced by Baku as an “act of terrorism”.
Iran's army recently conducted military exercises near the shared border as Azerbaijan draws closer to Israel, drawing ire from Tehran.
Azeri officials said embassy staff would be pulled from Tehran and Iran's ambassador summoned over the incident.
Tehran has come under heightened scrutiny in recent months after its brutal suppression of anti-government protests and its drone supplies to Russia.
Moscow has used Iran's Shahed loitering, self-detonating drones against Ukrainian civilians.
Ukrainian officials referenced Saturday's attack, with an adviser to President Volodymyr Zelenskyy saying Kyiv warned there would be repercussions from Iran's support for Russia.
“The logic of war is relentless and murderous. And issues hard bills to authors and co-conspirators,” tweeted Mr Zelenskyy's adviser Mykhailo Podolyak, citing “panic” in Moscow.
“Explosive night in Tehran: drone and missile industries, oil refineries,” he said. “Ukraine did warn you.”
The attack also follows US-Israeli military drills intended to project a strong front against Tehran and its growing nuclear threat, while CIA chief William Burns made an unannounced visit to Israel.
The five-day joint exercises, the most significant in recent years, involved planes used to strike hard-to-reach nuclear sites, analysts said.
On Thursday, the former chief of Israel's navy said it was better to attack Iran “sooner rather than later”.
“In my understanding, I think Israel has to attack, because the situation right now is that Iran is a threshold country — 100 per cent,” Vice Admiral Eliezer Marum told i24.
Tehran has ignored repeated calls to halt its nuclear programme, breaching commitments it made under the defunct 2015 nuclear deal in exchange for reduced sanctions.
It has increased its stockpile of highly-enriched uranium and installed advanced centrifuges at several sites, despite UN warnings over uranium traces at several undeclared locations.
With reporting by Sunniva Rose in Brussels