Iran has launched retaliatory air strikes at Israel, with explosions heard in Jerusalem and Tel Aviv, the country's two biggest cities, following Israel's biggest-ever military strike against Iran.
Air raid sirens sounded across Israel as authorities urged the public to take shelter.
Missiles were seen over Tel Aviv's skyline, with the military saying Iran had fired two salvos.
The US military has helped shoot down Iranian missiles that were headed toward Israel, two US officials said on Friday.
In the Tel Aviv area, Israel's ambulance service said five people were treated for shrapnel injuries.
Live footage of Tel Aviv showed what appeared to be a missile hitting an urban area.
A critically injured woman was admitted to Beilinson Hospital in nearby Petah Tikva, a hospital spokesperson said.
Iranian state news agency IRNA said Iran launched hundreds of ballistic missiles at Israel after Israel blasted Iran's huge Natanz underground nuclear site and killed its top military commanders.
Israel's military said Iran fired fewer than 100 missiles and most were intercepted or fell short.
"A limited number of buildings were affected, some of them as a result of shrapnel from the interception operations," the Israeli military's Arabic-language spokesman Avichay Adraee said in a post on X
Israel said its strikes were the start of "Operation Rising Lion".
Iran's Supreme Leader Ayatollah Ali Khamenei accused Israel of having started the strikes and initiating a war.
US President Donald Trump said it was not too late for Iran to halt the bombing campaign by reaching a deal on its nuclear program.
As evening fell on Friday, Iranian media reported explosions on the northern and southern outskirts of Tehran and at Fordow, near the holy city of Qom, a second nuclear site which had been spared in the first wave of attacks.
Air defences were activated across Tehran and explosions could be heard in Isfahan.
Israel's military said it was striking Iranian missile and drone launching sites, and had struck another nuclear site in Isfahan.
Israeli Prime Minister Benjamin Netanyahu said the Israeli campaign was aimed at defeating an existential threat from Iran, invoking the failure to halt the Holocaust in World War II.
Israel's operation "will continue for as many days as it takes to remove this threat," he said in a TV address.
"Generations from now, history will record our generation stood its ground, acted in time and secured our common future."
In a phone interview with Reuters, Trump said it was not clear if Iran's nuclear program had survived.
He said nuclear talks between Iran and the United States, scheduled for Sunday, were still on the agenda although he was not sure if they would take place.
"We knew everything," Trump said of the Israeli attack plans.
"I tried to save Iran humiliation and death. I tried to save them very hard because I would have loved to have seen a deal worked out," Trump said.
"They can still work out a deal, however, it's not too late."
Earlier, Trump posted on Truth Social: "Iran must make a deal, before there is nothing left."
Israel's National Security Adviser Tzachi Hanegbi said military action by itself would not destroy Iran's nuclear program but could "create the conditions for a long-term deal, led by the United States" to get rid of it.
Two regional sources said at least 20 Iranian military commanders were killed, a stunning decapitation reminiscent of Israeli attacks that swiftly wiped out the leadership of Lebanon's once-feared Hezbollah militia last year.
Iran also said six of its top nuclear scientists had been killed.
Among the generals killed on Friday were the armed forces chief of staff, Major General Mohammad Bagheri, and the Revolutionary Guards chief Hossein Salami.
Major General Mohammad Pakpour, swiftly promoted to replace Salami as Guards commander, vowed retaliation in a letter to the Supreme Leader read out on state television: "The gates of hell will open to the child-killing regime."
Iranians described an atmosphere of fear and anger, with some people rushing to change money and others seeking a way out of the country to safety.
Iranian media showed images of destroyed apartment blocks, and said nearly 80 civilians were killed in attacks that targeted nuclear scientists in their beds and wounded more than 300 people.
Israel said a missile fired from Yemen - whose Houthi militia are one of the last remaining Iranian-aligned groups still able to fire at Israel - had landed in Hebron in the occupied West Bank.
The Palestinian Red Crescent said three Palestinian children were wounded by shrapnel there.
Israel said that Iran had launched about 100 drones towards Israeli territory on Friday but Iran denied this and there were no reports of drones reaching Israeli targets.
The United Nations Security Council was due to meet on Friday at Iran's request.
Iran said in a letter to the Council that it would respond decisively and proportionally to Israel's "unlawful" and "cowardly" acts.
Israeli officials said it may be some time before the extent of damage to the underground nuclear site at Natanz is clear, where Iran has refined uranium to levels some countries have long said are suitable for a bomb rather than civilian use.
Iran has long insisted its nuclear program is for civilian purposes only.