Iranian state media reports explosions heard at airport in central Iran

Iranian state media has reported that explosions have been heard at Isfahan airport in central Iran, amid conflicting reports from United States and Iranian officials about what caused them.

Sources told the FARS news agency that the country's air defence system has been activated in Isfahan province against "an object suspected to be a drone".

"The sound of three explosions has been heard near an army base in north-west Isfahan," the sources reportedly said.

"At around 12:30am GMT (10:30am AEDT), three drones were observed in the sky over Isfahan. The air defence system became active and destroyed these drones in the sky," Iranian state TV added.

A senior commander of Iran's army, Siavosh Mihandoust, said, according to state TV, that no damage was caused in the overnight attack.

It comes as a US official told US broadcaster ABC that missiles were fired by Israel.

This assertion was disputed by an Iranian official who told Reuters that the explosions heard in Isfahan were a result of Iran firing its air defence batteries.

The Iranian official added that no missile attack was carried out against Iran.

The US official could not confirm whether Syria and Iraq were hit as well, after initial reports that explosions were also heard at those sites.

The Israeli military said that warning sirens which sounded early on Friday in northern Israel were a false alarm. 

The Australian government has updated its travel advice for Iran, which already had a "do not travel" warning in place, saying "regional tensions are high, and the security situation could deteriorate quickly with little or no notice". 

The Department of Foreign Affairs and Trade (DFAT) also updated its advice for Israel and the Occupied Palestinian Territories to leave "if it's safe to do so".

It said there was a "high threat of military reprisals and terrorist attacks against Israel and Israeli interests across the region". 

While DFAT had already advised Australians to reconsider their need to travel to Israel and had warned against travel near Gaza or the West Bank beyond East Jerusalem, the request to leave is new.

It added that Tel Aviv's Ben Gurion International Airport could "pause operations due to heightened security concerns at any time, and at short notice".

Flights were seen diverting away from Iran's Isfahan province.(Supplied: Flightradar24)

Earlier, flight tracking websites showed multiple flights being diverted away from Iranian airspace.

Iran closed its airports in Tehran, Shiraz and Isfahan after the incident and cleared flights from the western portion of its airspace for a few hours after the attack, according to flight tracking website FlightRadar24.

By 4:45am GMT (3:45pm AEDT), the airports and airspace had reopened, and closure notices posted on a US Federal Aviation Administration database had been removed.

Before the airports reopened, Flydubai said it had cancelled its Friday flights to Iran. One of its earlier flights turned back to Dubai, it had said.

The reports come just days after Iran launched hundreds of drones and missiles towards Israel, pictured.(Reuters: Ronen Zvulun)

According to Reuters, several Iranian nuclear sites are located in Isfahan province, including Natanz, which is considered the centrepiece of Iran's uranium enrichment program.

The International Atomic Energy Agency said it was monitoring the situation closely and that there was no damage to the nuclear sites.

Over the weekend, Iran launched hundreds of drones and missiles in a retaliatory strike after a suspected Israeli strike on its embassy compound in Syria.

Most of the drones and missiles were downed before reaching Israeli territory.

Israel had said it was going to retaliate against Iran's April 13 missile and drone attack.

ABC/wires