Thousands of fighters from Iran-backed groups in the Middle East are ready to come to Lebanon to join with the militant Hezbollah group in its battle with Israel if the simmering conflict escalates into a full-blown war, officials with Iran-backed factions and analysts say.

Almost daily exchanges of fire have occurred along Lebanon’s frontier with northern Israel since fighters from the Hamas-controlled Gaza Strip staged a bloody assault on southern Israel in early October that set off a war in Gaza.

The situation to the north worsened this month after an Israeli airstrike killed a senior Hezbollah military commander in southern Lebanon.

Hezbollah retaliated by firing hundreds of rockets and explosive drones into northern Israel.

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Houthi fighters march during a rally of support for the Palestinians in the Gaza Strip and against the US strikes on Yemen outside Sanaa in January (AP Photo, File)

Israeli officials have threatened a military offensive in Lebanon if there is no negotiated end to push Hezbollah away from the border.

Over the past decade, Iran-backed fighters from Lebanon, Iraq, Afghanistan and Pakistan fought together in Syria’s 13-year conflict, helping tip the balance in favour of Syrian President Bashar Assad.

Officials from Iran-backed groups say they could also join together again against Israel.

Hezbollah leader Hassan Nasrallah said in a speech on Wednesday that militant leaders from Iran, Iraq, Syria, Yemen and other countries have previously offered to send tens of thousands of fighters to help Hezbollah, but he said the group already has more than 100,000 fighters.

“We told them, thank you, but we are overwhelmed by the numbers we have,” Mr Nasrallah said.

Mr Nasrallah said the battle in its current form is using only a portion of Hezbollah’s manpower, an apparent reference to the specialised fighters who fire missiles and drones.

But that could change in the event of an all-out war. Mr Nasrallah hinted at that possibility in a speech in 2017 in which he said fighters from Iran, Iraq, Yemen, Afghanistan and Pakistan “will be partners” of such a war.

Officials from Lebanese and Iraqi groups backed by Iran say Iran-backed fighters from around the region will join in if war erupts on the the Lebanon-Israel border. Thousands of such fighters are already deployed in Syria and could easily slip through the porous and unmarked border.

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Destroyed houses in Khiam, a town near the Lebanese-Israeli border, that was hit by Israeli air strikes on Friday (Hussein Malla/AP)

Some of the groups have already staged attacks on Israel and its allies since the Israel-Hamas war started October 7. The groups from the so-called “axis of resistance” say they are using a “unity of arenas strategy” and they will only stop fighting when Israel ends its offensive in Gaza against their ally, Hamas.

“We will be (fighting) shoulder to shoulder with Hezbollah” if an all-out war breaks out, one official with an Iran-backed group in Iraq told The Associated Press in Baghdad, insisting on speaking anonymously to discuss military matters. He refused to give further details.

The official, along with another from Iraq, said some advisers from Iraq are already in Lebanon.

Eran Etzion, former head of policy planning for the Israeli Ministry of Foreign Affairs, said at a panel discussion hosted by the Washington-based Middle East Institute on Thursday that he sees “a high probability” of a “multi-front war”.

He said there could be intervention by the Houthis and Iraqi militias and a “massive flow of jihadists from (places) including Afghanistan, Pakistan” into Lebanon and into Syrian areas bordering Israel.

Daniel Hagari, Israel’s military spokesman, said in a televised statement this past week that since Hezbollah started its attacks on Israel on October 8, it has fired more than 5,000 rockets, anti-tank missiles and drones toward Israel.

“Hezbollah’s increasing aggression is bringing us to the brink of what could be a wider escalation, one that could have devastating consequences for Lebanon and the entire region,” Mr Hagari said.

“Israel will continue fighting against Iran’s axis of evil on all fronts.”

Hezbollah officials have said they do not want an all-out war with Israel but if it happens they are ready.