Iranian state media said air defence batteries had been fired in several provinces, with three drones destroyed over the central city of Isfahan, which is home to a major military airbase and nuclear facilities.

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

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A source familiar with the situation has described the operation as a strike.

Speaking to Sky News' US partner NBC, they said Israel was currently assessing its effectiveness and the damage it has caused.

The attack also coincided with the birthday of Iran's supreme leader, Ayatollah Ali Khamenei.

The Israeli military has declined to comment on the claims.

The strike comes amid heightened tensions in the Middle East region after Iran's unprecedented missile-and-drone attack on Israel.

There has been no damage to Iran's nuclear sites according to the UN's nuclear watchdog.

The International Atomic Energy Agency said it is monitoring the situation "very closely" and called for "extreme restraint".

Analysis:
Retaliation appears to have been carefully chosen

Sky News' military analyst Michael Clarke said Isfahan "would make sense" as a target as it's home to one of the least sensitive nuclear sites.

"It's a research site, about 3,000 or so scientists work there and there's no evidence this was targeted on the nuclear site," he added.

"But the fact that Isfahan is one of the cities that does quite a lot of nuclear work is also symbolically quite important, I think, if the Israelis are indicating that they're not frightened to go after these sites."

Isfahan is more than 1,000 miles from Israel, which suggests this was not a drone attack, Mr Clarke said, adding it was "almost certainly" led by Jericho missiles.

Dubai-based carriers Emirates and FlyDubai began diverting around western Iran at about 4.30am local time.

Iran also grounded commercial flights in Tehran and across areas of its western and central regions.