Israel has reportedly retaliated for last weekend's drone and missile strike by Iran.
Iranian media is reporting an explosion was heard at an air base in the central city of Isfahan.
Tehran says it fired air defence systems overnight, with local residents saying they spotted drones.
US network NBC News reports Israel carried out an operation in Iran, citing a person familiar with the matter.
The network says the US was informed of the operation in advance.
A view of Shaikh Lutfallah Mosque in Isfahan, Iran, 12-5-15. Image: B.O'Kane / AlamyEarly indications suggest they were limited strikes on deliberately chosen targets.
One strike appears to have been on an airbase outside Isfahan which is connected to Iran's aircraft manufacturing industry - which would have been carefully chosen as a response to the drones flown at Israel on Saturday night.
Iran flew more than 300 drones and missiles at Israel in retaliation for the bombing of its consulate in Damascus earlier this month.
Most of these were intercepted before they reached Israeli airspace and the ones that got through caused minimal damage to an airbase.
Isfahan is close to one of Iran's nuclear facilities although this doesn't appear to be an attack on the nuclear site.
Iranian state TV said its nuclear facilities remain unharmed, Reuters news agency reported.
The timing of the attack, around 4am local time in Iran, is likely to see limited casualties.
Air defences
Iran's state-run IRNA news agency said its air defences fired across several provinces, while the country's senior commander Siavosh Mihandoust said no damage has been caused.
He claimed an explosion came from air defence systems targeting "one suspicious object".
Iranian state TV said three drones were "destroyed" over Isfahan shortly after midnight, but later said the situation in the city is normal and no ground explosions had occurred.
Iran has grounded commercial flights across parts of the country after reports of explosions.
State media also said Iran fired its air defence systems after reports of blasts near the city of Isfahan, which forced the country to impose flight restrictions.
Tasnim, a state news agency, reports air traffic has since been cleared to resume at some airports.
Dubai-based carriers Emirates and FlyDubai began diverting around western Iran at about 4.30am local time.
They did not explain the reason, though local warnings suggested the airspace may have been closed.
Israel's military has not commented but had promised a response to Iran's attack over the weekend.
Tensions remain high in the Middle East after Iran's missile and drone attack on Israel over the weekend, which came after Israel struck the Iranian embassy in Syria on April 1st.
The Iranian Embassy in Dublin told Newstalk any Israeli retaliation to Iran would be met with a ‘strong and severe’ response.
