Iran and Israel traded missiles and airstrikes on Saturday, the day after Israel launched a sweeping air offensive against its old enemy, killing commanders and scientists and bombing nuclear sites in a stated bid to stop it building an atomic weapon.
Iran had vowed to avenge Friday's Israeli onslaught, which gutted Iran's nuclear and military leadership and damaged atomic plants and military bases, killing 78 people including civilians according to Iran's U.N. envoy.
Iran's overnight fusillade included hundreds of ballistic missiles and drones, an Israeli official said. Three people, including a man and a woman, were killed and dozens wounded, the ambulance service said.
Tehran warned Israel's allies that their regional military bases would come under fire too if they help shoot down Iranian missiles, Iranian state television reported.
In Israel, air raid sirens sent residents into shelters as waves of missiles streaked across the sky and interceptors rose to meet them, killing at least three people. An Israeli official said Iran had fired around 200 ballistic missiles in four waves.
U.S. President Donald Trump has lauded Israel's strikes and warned of much worse to come unless Iran quickly accepts the sharp downgrading of its nuclear programme that the U.S. has demanded in talks that had been due to resume on Sunday.
But with Israel saying its operation could last weeks, and urging Iran's people to rise up against their Islamic clerical rulers, fears have grown of a regional conflagration dragging in outside powers, with global economic and financial repercussions.
The United States, Israel's main ally, helped shoot down Iranian missiles, two U.S. officials said.
Iranian fire still struck residential districts in Israel, however, and Defense Minister Israel Katz said Iran's leadership had crossed a red line.
"If (Supreme Leader Ayatollah Ali) Khamenei continues to fire missiles at the Israeli home front, Tehran will burn," he said in a statement.
Gulf Arab states that have long mistrusted Iran but fear coming under attack in any wider conflict have urged calm as worries about disruption to the Gulf region's crucial oil exports boosted the price of crude by about 7% on Friday.
With Iran's air defences heavily damaged, chief of staff Tomer Bar said "the road to Iran has been paved".
In preparation for possible further escalation, reservists were being deployed across Israel. Army Radio reported units had been positioned along the Lebanese and Jordanian borders.
In Iran, explosions were heard overnight across the capital, state media reported. Fars News agency said two projectiles had hit Mehraband airport, located inside the capital, which is both civilian and military.
State television reported that a 14-storey housing complex, Shahid Chamran, had been flattened by a missile. It said 60 people had been killed, though there was no immediate official confirmation.