Israel's military says Iran has launched dozens of drones towards Israel. The Israeli Defence Forces says it will take hours before the drones enter Israeli airspace.

Israel had put its military on high alert and called off school trips and other youth activities in preparation.

A number of drones were seen flying from the direction of Iran over Iraq's Sulaymaniya province, three security sources told Reuters on Saturday.

"Dozens of drones were spotted flying from Iran in the direction of Israel over Iraqi airspace," two Iraqi security sources also told Reuters.

Iraq also announced shutting down its airspace and suspending all air traffic on Saturday, Iraq's transport ministry told the country's state-owned news agency.

Jordan had also begun temporarily closing its airspace for several hours beginning at 11pm local time (6am AEST) to all incoming, departing and transit aircraft, state-owned Al-Mamlaka news said on Saturday.

The country's air defences were ready to intercept and shoot down any Iranian drones or aircraft that violate its airspace, two regional security sources said, adding the army was also in a state of high alert and radar systems were monitoring drone activity.

The United States confirmed Iran began an airborne attack against Israel and said it is likely to unfold over a number of hours.

Israel's Prime Minister Benjamin Netanyahu said the country's "defensive systems are deployed; we are ready for any scenario, both defensively and offensively."

"We have determined a clear principle: Whoever harms us, we will harm them. We will defend ourselves against any threat and will do so level-headedly and with determination," he told people in a video message.

Israel's Prime Minister Benjamin Netanyahu said the country's "defensive systems are deployed; we are ready for any scenario, both defensively and offensively."

"We have determined a clear principle: Whoever harms us, we will harm them. We will defend ourselves against any threat and will do so level-headedly and with determination," he told people in a video message.

He also thanked the US for "standing alongside Israel, as well as the support of Britain, France and many other countries."

US President Joe Biden, who on Friday warned Iran against attacking Israel after saying such a scenario appeared imminent, has pledged to stand with Israel against Iran, the White House said.

Explosives-laden drones:

Israel's top-rated Channel 12 TV reported that Iran had launched a total of around 100 drones and cruise missiles at Israeli targets and that some were shot down over Syria or Jordan.

The Israeli military said Iran launched more than 100 explosives-laden drones at Israel since Saturday but declined to immediately confirm media reports that cruise missiles were also part of the salvo.

A retired Israeli general, Amos Yadlin, told the Channel that the Iranian drones were equipped with 20kg (44 pounds) of explosives each.

Mr Netanyahu convened the Israeli war cabinet at military headquarters in Tel Aviv, his office said early on Sunday.

Airspaces shut down:

Iraq also announced shutting down its airspace and suspending all air traffic on Saturday, Iraq's transport ministry told the country's state-owned news agency.

Jordan closed down its airspace ahead of the attack to all incoming, departing and transit aircraft, state-owned Al-Mamlaka news said on Saturday, leading to many people being stuck at the airport.

Residents in several cities in the northern part of the country near Syria and central and southern areas heard heavy aerial activity. A security source said the country's air force was intensifying reconnaissance flights.

Israel closed its airspace as a precaution, with its carrier El Al Airlines saying it cancelled 15 flights scheduled for Saturday and Sunday, affecting several destinations.

Syria put on high alert its Russian-made Pantsir ground-to-air defence systems around the capital Damascus and major bases in the event of an Israeli strike, army sources said.

They said they expected Israel would retaliate against army bases and installations where pro-Iranian militia were based after Iran's elite Revolutionary Guards said they launched dozens of drones and missiles against specific targets in Israel.

Lebanon's Al Jadeed TV also said the country has closed its airspace.

Iranian Defence Minister Mohammad Reza Ashtiani warned that Tehran would firmly respond to any country that "opens its airspace or territory for attacks on Iran by Israel", Iran's semi-official Mehr news agency reported on Sunday.

UK Prime Minister Rishi Sunak said on Saturday he condemned Iran's "reckless" attack against Israel, which he said showed "intent on sowing chaos in its own backyard".

"These strikes risk inflaming tensions and destabilising the region," Sunak said in a statement.

The Egyptian foreign ministry, in a statement early on Sunday, called for the exercise of "utmost restraint" to spare the region and its people from further factors of instability and tension.

Iran seized cargo ship:

The drone attack came shortly after Iran's Revolutionary Guards seized an Israeli-linked cargo ship in the Strait of Hormuz, days after Tehran said it could close the key trade route.

Iran's state-run IRNA news agency reported that a Guards helicopter had boarded and taken into Iranian waters the Portuguese flagged MSC Aries, saying it was linked to Israel.

MSC, which operates the Aries, confirmed Iran had seized the ship and said it was working "with the relevant authorities" for its safe return and the wellbeing of its 25 crew.

MSC leases the Aries from Gortal Shipping, an affiliate of Zodiac Maritime, Zodiac said in a statement, adding that MSC is responsible for all the vessel's activities.

Zodiac is partly owned by Israeli businessman Eyal Ofer.

Video on Iranian news channels purporting to show the seizure included a figure abseiling from a helicopter on to a ship.

An Indian government official, speaking on condition of anonymity because he was not authorised to brief to journalists, said 17 of the crew were Indians.

Israeli Foreign Minister Israel Katz accused Tehran of piracy.

Sources | Reuters/ABC