Iran has launched retaliatory airstrikes at Israel, with explosions heard in Jerusalem and Tel Aviv, following Israel's biggest-ever military strike against its longstanding enemy.
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.
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.
The unprecedented Israeli strikes on Iran and the subsequent Iranian retaliation raised concerns about a broader regional conflagration, although Iran's allies Hamas in Gaza and Hezbollah in Lebanon, have been decimated by Israel.
Iran's 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.
Iran's Supreme Leader Ayatollah Ali Khamenei accused Israel of having initiated a war.
A senior Iranian official said nowhere in Israel would be safe and revenge would be painful.
Israel's operation "will continue for as many days as it takes to remove this threat," Israeli Prime Minister Benjamin Netanyahu said in a TV address.
Mr Netanyahu, who for decades has raised the alarm about Iran's nuclear programme, said he authorised the air assault in an effort to prevent Iran from building nuclear weapons.
Israel and its Western allies have said this is Iran's objective but Iran has denied it.
In a video issued by his office, Mr Netanyahu appealed to the Iranian people to stand up against their leaders.
"I am with you, the Israeli people are with you," he said.
"Generations from now, history will record our generation stood its ground, acted in time and secured our common future," Mr Netanyahu said.
Iran has long insisted its nuclear programme is for civilian purposes only.
The UN nuclear watchdog concluded this week that it was in violation of its obligations under the global non-proliferation treaty.
US President Donald Trump said it was not too late for Iran to halt the Israeli bombing campaign by reaching a deal on its nuclear programme.
Iran had been engaged in talks with the Trump administration on a deal to curb its nuclear programme to replace one that Trump abandoned in 2018.
Follow live developments as tensions escalate in the Middle East
Iran had rejected the last US offer.
Iranian media showed images of destroyed apartment blocks in Iran, and said nearly 80 civilians were killed in attacks that targeted nuclear scientists in their beds and wounded more than 300 people.
Israel's military said it was striking Iranian missile and drone launching sites, and had struck another nuclear site in Isfahan.
An Israeli military spokesperson denied Iranian media reports that an Israeli fighter jet was downed with a pilot detained.
In a phone interview with Reuters, Mr Trump said nuclear talks between Iran and the United States, scheduled for Sunday, were still on the agenda though he was not sure if they would take place.
"We knew everything," Mr 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," he said.
"They can still work out a deal, however, it's not too late."
Israeli National Security Adviser Tzachi Hanegbi said military action by itself would not destroy Iran's nuclear programme, 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 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 on state television: "The gates of hell will open to the child-killing regime."
Watch: Benjamin Netanyahu says Israeli strikes seek to hurt Iran's nuclear infrastructure
Read more:
What we know so far about the Israeli strikes on Iran
Iran's nuclear programme - the key sites and locations
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.
"People on my street rushed out of their homes in panic. We were all terrified," said Marziyeh, 39, who was awakened by a blast in Natanz.
While some Iranians quietly hoped the attack would lead to changes in Iran's hardline clerical leadership, others vowed to rally behind the authorities.
"I will fight and die for our right to a nuclear programme. Israel and its ally America cannot take it away from us with these attacks," said Ali, a member of the pro-government Basij militia in Qom.
Watch: Footage shows buildings ablaze in Tehran
Iran's ability to retaliate with weapons fired by its regional proxies has been sharply degraded over the past year, with the downfall of its ally Bashar al-Assad in Syria and the decimation of Hezbollah in Lebanon and Hamas in Gaza.
Israel said a missile fired from Yemen, whose Houthi militia are Iran-aligned, 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 launched around 100 drones towards Israeli territory earlier, but Iran denied this and there were no reports of drones reaching Israeli targets.
The United Nations Security Council was due to meet 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.
The price of crude LCOc1 leaped on fears of wider retaliatory attacks across a major oil-producing region, although there were no reports that oil production or storage was damaged.
OPEC said the escalation did not justify any immediate changes to oil supply.
An Israeli security source said Mossad commandos had been operating deep inside the Islamic Republic before the attack, and the Israeli spy agency and military had mounted a series of covert operations against Iran's strategic missile array.
Israel also established an attack-drone base near Iran, the source added.
The military said it had bombarded Iran's air defences, destroying "dozens of radars and surface-to-air missile launchers".
Israeli officials said it may be some time before the extent of damage to the underground nuclear site at Natanz is clear.
Western countries have long said Iran refined uranium there to levels suitable for a bomb rather than civilian use.
Later, Iranian media reported explosions on the northern and southern outskirts of Iran and at Fordow, near the holy city of Qom, a second nuclear site that was spared in the first wave of attacks.
'No Irish citizen should travel to Israel' -Tánaiste
Tánaiste Simon Harris has said that no Irish citizens should travel to Israel in the wake of attacks on Iran.
The Government has updated its travel advice to Israel since the attacks, advising citizens against travel to Israel.
Speaking on RTÉ's News at One, he said that this was an extension of advice that was already in place for Iran.
"We're keeping in close contact with our diplomatic teams on the ground in Iran and Israel, but I would ask all Irish citizens to heed that updated travel advice," he said.
The Irish Department of Foreign Affairs has updated its security advice for Israel to 'Do Not Travel'.
The department says significant disruption is to be expected at airports in Israel.
Earlier, Tánaiste and Minister for Foreign Affairs Simon Harris has said that the Middle East "desperately needs peace and stability".
"I urge restraint and de-escalation by all involved, and for those with influence to use it positively at this critical moment," he said.
Mr Harris also said that his officials were in touch with the Irish embassy in Tehran regarding the safety of the small Irish community there.
