The Israeli military has confirmed that nearly 200 missiles have been launched from Iran into Israel.
Tehran fired a barrage of ballistic missiles at Israel on Tuesday in retaliation for Israel's campaign against Iran’s Hezbollah allies in Lebanon.
Alarms sounded across Israel and explosions could be heard in Jerusalem and the Jordan River valley after Israelis piled into bomb shelters.
Israeli army radio said nearly 200 missiles had been launched into Israel from Iran. Israel's military later sounded the all-clear and said residents were free to leave their shelters.
Details of damage and casualties remained unclear but US National security adviser Jake Sullivan said in a press conference the attack was “defeated and ineffective”.
Iran's Revolutionary Guards said Iran had launched tens of missiles at Israel, and that if Israel retaliated Tehran's response would be "more crushing and ruinous".
But Israeli military spokesman Daniel Hagari said the attack would have consequences, as did Israel's UN Ambassador Danny Danon.
"As we have previously made clear to the international community, any enemy that attacks Israel should expect a painful response", Danon said in a statement.
It comes after Israel announced it is carrying out “limited” and “targeted” ground raids on Hezbollah in Lebanon in a major escalation of a conflict in the Middle East that now threatens to suck in the US and Iran.
The Israeli military said operations in Lebanon began on Monday night and involved paratroops and commandos from the elite 98th division, which was deployed to the northern front two weeks ago from Gaza where they had been fighting for months.
It said its air force and artillery supported ground troops engaged in “limited, localised, and targeted ground raids” against Hezbollah in southern Lebanon villages that posed “an immediate threat to Israeli communities in northern Israel”.
The Israeli military warned people to evacuate nearly two dozen Lebanese border communities hours after announcing its ground operations against Hezbollah.
Meanwhile the UK Government has chartered a flight out of Lebanon Britons wanting to leave.
Foreign Secretary David Lammy described the situation in Lebanon as “volatile” and with the “potential to deteriorate quickly” as the flight, due to leave Beirut-Rafic Hariri International Airport on Wednesday, was confirmed.
Earlier, Mr Lammy reiterated calls for Britons in Lebanon to leave and said the Government will do “all that we can” to assist people in fleeing.