Air defences were fired in several provinces, including from a major military airbase and nuclear facilities near the central city of Isfahan, where state media said three drones had been shot down.

So far, there have not been any reports of damage or casualties.

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Israel has declined to comment, but a US source familiar with the situation has it as a strike.

The US told a meeting of G7 ministers on Friday that it had been "informed at the last minute" by Israel about the attack, which coincided with the birthday of Iran's supreme leader, Ayatollah Ali Khamenei.

Meanwhile, Iran has no plans for immediate retaliation and sought to downplay the military operation.

A senior official said the country was looking at it more as an "infiltration" rather than an "external attack".

Iranian President Ebrahim Raisi had previously warned Tehran would deliver a "severe response" to any hostile action.

The US and other countries, including the UK, had also urged Israel not to respond to Iran's recent assault, which followed an airstrike on Iran's embassy in Syria's capital, Damascus.

Speaking at the meeting of G7 foreign ministers on the Italian island of Capri, US secretary of state Antony Blinken repeatedly refused to be drawn on the attack on Iran.

He said: "I'm not going to speak to that except to say that the United States has not been involved in any offensive operations."

Mr Blinken went on: "All I can say is that for our part, and for the entire G7, our focus has been on de-escalation, on avoiding a larger conflict."

It comes amid heightened tensions in the Middle East, as Israel continues its war against Iranian-backed Hamas in Gaza, launched after the deadly incursion by the militant group on 7 October.

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The airbase in Isfahan has long been home to Iran's fleet of American-made F-14 Tomcat fighter jets, bought before the 1979 Islamic Revolution.

Isfahan also hosts the biggest nuclear research establishment in the country.

Although Tehran says its nuclear work is peaceful, the West believes the regime aims to build a weapon.

Iranian state media television said the facilities near the city were "fully safe".

The UN's nuclear watchdog, the International Atomic Energy Agency, also said there was no damage to nuclear facilities but said it was monitoring the situation "very closely" and called for "extreme restraint".

Iran shut its airports in Tehran, Shiraz and Isfahan and also closed the western portion of its airspace for several hours after the strike.

The US Embassy in Jerusalem imposed travel restrictions on government employees "out of an abundance of caution".

Around the same time, Israeli warplanes flying over Syria's southern province of Daraa struck a military radar for government forces after it spotted the fighter jets, according to the British-based Syrian Observatory for Human Rights.

Separately, the US and Britain have announced a fresh round of sanctions on Iran.

The moves came as European Union leaders meeting in Brussels pledged to ramp up sanctions on Iran to target its drone and missile deliveries to proxies in Gaza, Yemen and Lebanon.