LEBANON will be bombed "back to the Stone Age" if Hezbollah unleashes missiles and drones into Israel, a former government adviser has warned.
The Iran-backed militant group has vowed to join the war in support of Hamas "when the time comes" in what would be a huge escalation.
Foreign powers have urged Hezbollah to stay put on the sidelines to stop a new front opening up and the raging conflict spilling into another country.
Until now, Israeli forces and armed groups in Lebanon have exchanged low-level cross-border fire.
Earlier this week, Israel ordered civilians in 28 areas to evacuate amid fears Hezbollah is on the brink of invading.
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Israel considers Hezbollah an even bigger threat than Hamas, with the group heavily armed with weapons supplied by Iran.
Hezbollah's deputy chief Naim Qassem has already insisted its militants have been readied to enter the conflict "when the time comes for action".
He warned: "Hezbollah knows its duties perfectly well.
"We are prepared and ready, fully ready, and we are following developments moment by moment."
But Israel has threatened to retaliate aggressively should Hezbollah become more deeply involved.
Yigal Carmon, former counter-terrorism advisor to Israeli prime ministers Yitzhak Shamir and Yitzhak Rabin, said Lebanon will suffer severe consequences.
He told The Sun: "We told them [Hezbollah] several times that if they intervene Israel will bring them to the Stone Age.
"We will take Lebanon back to the Stone Age."
Mr Carmon, who is president and founder of the Middle East Media Research Institute, said Israel will discharge a barrage of bombs into Lebanon to wipe out vital infrastructure.
He added: "How do you bring a nation to the Stone Age?
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"One or two planes will go to Lebanon with the minimum number of casualties.
"They will bomb the sewage, the water and the electricity centers of Lebanon, of Beyrouth.
"Imagine a city like Beyrouth, with two million people, without sewage. This would be the Stone Age.
"And Nasrallah, the secretary general of Hezbollah, knows that."
Mr Carmon said he hopes Israel's plan is enough to deter Hezbollah from deploying its terrifying arsenal.
Lt Col Peter Lerner, a spokesman for the IDF, said Hezbollah should be “very cautious” of interfering.
He said: "With Hezbollah, we have had several skirmishes along the border over the last few days.
"I would highly recommend that Hezbollah watch very closely what is happening to Hamas and their organisation in Gaza as we speak."
Armed with a huge and diverse stockpile of unguided artillery rockets, ballistic, antiair, antitank, and anti-ship missiles, Hezbollah is considered the world’s most heavily armed non-state actor.
Iran's shadowy Revolutionary Guard founded Hezbollah in 1982, in the middle of Lebanon's civil war from 1975 to 1990.
Sharing Tehran's Shi'ite Islamist ideology, Hezbollah then recruited Lebanese Shi'ite Muslims.
Now deemed a terrorist organisation by the US and some Western governments, the group has risen from a shady faction to a heavily armed force with major sway over the Lebanese state.
Hezbollah boasts a horrifying collection of weapons, including precision rockets and drones.
The group claims it can strike all parts of Israel and has deep ties with Hamas and Islamic Jihad, another Palestinian faction backed by Iran.
Iran is believed to allocate hundreds of millions of pounds a year to propping up Hezbollah with weapons and cash influxes.
Hezbollah's arsenal grew rapidly after its five-week war with Israel and intelligence sources believe the group was armed with more than 150,000 rockets as of July 2016.
It is thought its rocket collection has since swelled even more - with most relatively small, short-range weapons that are easily portable.
One of Hezbollah's most intimidating rockets is the "Katyusha" series - inspired by Soviet designs.
They have a range of up to 25 miles, can carry warheads of up to 28 miles and are difficult to intercept thanks to their short flight time and low trajectory.
Hezbollah's rocket inventory also features much heavier rockets such as the Zelzal series.
With a range of up to 160 miles, they are able to blast targets much deeper in Israel and cause greater destruction.
Hezbollah also has a number of short-range ballistic and anti-ship missiles under its belt.
Iran has spent years fine-tuning its ballistic missiles - and has provided some to Hezbollah.
One such missile is the Fateh-110, able to strike up targets up to 186 miles away.
Iran has also aided Hezbollah with its drone arsenal.
The militant group has a large number of drones at its fingertips - including the Ayoud.
It has a range of at least 1,056 miles and an endurance of up to 24 hours.
