The US has told a United Nations briefing that Iran “will be held responsible” for its biggest missile attack on Israel – as the world braces to see how Israel will retaliate.

Israel has vowed payback for Iran’s assault on Wednesday (AEST) involving 180 ballistic missiles – most of which were intercepted by defence systems.

On Thursday (AEST), the US ambassador to the UN, Linda Thomas-Greenfield, emphasised America’s support for Israel and warned of the consequences of attacking its ally.

“Let me be clear: The Iranian regime will be held responsible for its actions,” she told a UN Security Council briefing on the Middle East crisis.

“We strongly warn against Iran – or its proxies – taking actions against the United States, or further actions against Israel.”

Iran said on Wednesday (local time) its missile barrage was over, barring further provocation, as Israel and the US promised to hit back hard.

US President Joe Biden said he did not support Israel targeting Iran’s nuclear sites. Biden said Israel had the right to respond but it should be proportional.

Asked “would you support an attack on Iran’s nuclear sites by Israel?”, Biden said: “The answer is no.”

“We’ll be discussing with the Israelis what they’re going to do, but all seven of us [G7 nations] agree that they have a right to respond but they should respond proportionally,” he said.

Israeli military chief Lieutenant General Herzi Halevi said the country’s defence force had the ability to attack “any point in the Middle East”.

“Those of our enemies who have not understood this until now, will understand it soon,” he said.

“We will respond, we know how to locate important targets, we know how to strike with precision and power.”

On Thursday, Israel renewed its bombardment of Beirut’s southern suburbs with more than a dozen airstrikes against what it said were Hezbollah targets.

Israel also carried out an air strike on a residential building in Syria’s capital Damascus, killing three civilians and injuring three, Syrian state media reported on Wednesday.

Israeli soldiers killed

Israel said eight of its soldiers had been killed in combat in south Lebanon, the deadliest loss on that front in the past year of border-area clashes.

Hezbollah said its fighters were engaging Israeli forces inside Lebanon, reporting ground clashes for the first time since Israeli forces pushed over the border.

“We are at the height of a difficult war against Iran’s Axis of Evil, which wants to destroy us,” Israeli Prime Minister Benjamin Netanyahu said in a condolence video.

“This will not happen because we will stand together and with God’s help, we will win together.”

Zakie Khoury Daou has lived in Lebanon with her family for seven years and says she’s not leaving. Photo: AAP

Aussies resist calls to flee Lebanon

Australians in Lebanon have been urged to leave as bombings escalate but some are hesitant to uproot their lives, despite conflict spreading across the Middle East.

Zakie Khoury Daou has lived in Lebanon for seven years after meeting her husband. Despite the unrest and uncertainty, she’s staying put.

Previously she had told her family back in Australia she was safe with confidence as clashes between Israel and designated terror group Hezbollah were mainly localised to the country’s south.

“Now it’s not just the south, it’s all over Lebanon,” she said from Beirut.

Living with her 29-year-old daughter and nine-year-old son, Khoury Daou said she saw smoke and fire from bombed areas in the distance and heard war planes overhead every day.

“It’s unbelievable how the sound travels in this city,” she said.

But she’s adamant sustained attacks from Israel and life grinding to a halt with everything but essential services effectively shut down “doesn’t give me reason to uproot my life and go back to Australia”.

There had been similar situations in the past where she had persevered, she said. Although she acknowledged a lot of uncertainty about what could happen.

Refugees have filled schools and flowed onto the streets and into empty and destroyed residential blocks. Some had even resorted to invading houses for shelter, Khoury Daou said.

“A whole building in central Beirut got hijacked by refugees.”

A building destroyed by an Israeli airstrike in Beirut’s south. Photo: Getty

More than 100 commercial airline tickets have been secured for Australians trying to leave Lebanon.

But with airlines halting flights and diverting away from Lebanese airspace, there are increasing concerns the international airport could shut.

Dozens of Australians left on flights on Monday and Tuesday, while another is scheduled for Thursday.

The Department of Foreign Affairs said it wasn’t aware of any Australians killed in Lebanon due to the conflict as of Wednesday.

“Australians in Lebanon should be prepared to leave quickly or shelter in place for an extended period,” a spokesperson said.

“If conditions worsen, we may not be able to assist all Australians remaining in Lebanon.”

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-with AAP