IRAN has vowed to unleash a weapon "never used before" against Israel if the country retaliates for Tehran's missile and drone blitz.
Israel told Iran today they won't get off "scot-free" for the attacks as the world waits with bated breath for their response amid fears of an "uncontrollable war" across the Middle East.
It comes as the US now believes Israel is planning a "narrow and limited strike" inside Iran.
But Iranian security chief Abolfazl Amouei last night warned that if Israel does respond then Tehran is "prepared to use a weapon that we have never used".
It is unclear what weapon Amouei was referring to, but he warned Israel to "act wisely" as it considers its next steps.
A chief IDF spokesman responded to the threats, vowing that Iran will face retaliation.
IDF spokesman Rear Admiral Daniel Hagari said: “We cannot stand still from this kind of aggression, Iran will not get [off] scot-free with this aggression.
“We will respond in our time, in our place, in the way that we will choose."
A senior administration official and another source familiar with the intelligence told CNN they understood Israel were considering attack Iran with a "limited strike".
The official told the US broadcaster: "We would hope that they would give us some warning so that we're prepared to protect our personnel, not just military but diplomatic throughout the region."
Rishi Sunak tonight warned Israeli prime minister Benjamin Netanyahu against "further significant escalation" in Tel Aviv's response to Iran's attack.
He tweeted: "Earlier today I spoke to Prime Minister @netanyahu and reiterated our support for Israel's security following Iran's reckless attack at the weekend.
"Further significant escalation will only deepen instability in the region.
"This is a moment for calm heads to prevail."
Colonel Hamish de-Bretton Gordon, a weapons and defence expert, said that Iran could be hinting at unleashing nuclear, biological and chemical warfare.
Yet, the retired army officer told The Sun: "It is unlikely that Iran has some new, wonderful weapon that nobody knows about that could really have an impact against Israel or the West.
"What I take from this is further bluster from Iran. They're obviously desperately concerned that the Israelis are going to hit them back hard."
On Saturday night, Iran attacked Israel with a wave of at least 330 ballistic and cruise missiles and drones - the first ever direct attack by Tehran on its enemy.
Iran had promised retaliation for a deadly strike on its consulate building in Damascus earlier this month, but its barrage failed to get through Israel's defences.
Israel Iron Dome defence system and its allies warplanes - including the UK's RAF Typhoons - shot down 99 per cent of the projectiles.
In response, Iran's deputy foreign minister, Ali Bagheri, raged last night: "If the enemy makes another mistake...they should know they will not have 12 days and Iran's response speed will be less than a few seconds".
Iran also yesterday vowed to launch ten times the amount of missiles in a fresh strike against Israel if it unleashes a retaliatory hit.
An attack ten times the size would see over 3,300 weapons hurled at Israel, including more than 1,400 missiles.
The recent threats mark another escalation in the blazing power battle between the two foes that is threatening to spark an all-out war across the region.
But Israel appears undeterred by Tehran's warnings as it confirmed again last night it will strike back.
De-Bretton Gordon argued that Iran's warnings are a clear sign of its fear.
"I think this is a cry from Tehran," he said, adding that the nefarious state will do all it can "to persuade Israel to do nothing and draw a line under it".
"It's clear that the Iranian air defence system is nowhere near capable of what Israel and her allies put together.
"Iran could take a heck of a thumping and it might well be that Israel decide to take out their nuclear capability as well."
This is the fear of the UN's nuclear watchdog chief who said yesterday he is "concerned" that Israel may target Iran's nuclear sites.
Rafael Grossi, head of the International Atomic Energy Agency (IAEA) urged "extreme restraint" from Israel.
He revealed that Iran temporarily closed its nuclear facilities over "security considerations" in the wake of its missile and drone attack.
They reopened on Monday but inspectors were kept away "until we see that the situation is completely calm".
Iran has long said its nuclear programme is peaceful but Western countries accuse Tehran of attempting to build nuclear bombs.
It comes as Israel Defence Forces (IDF) chief of staff, Lt Gen Herzi Halevi, said Israel will respond to Iran's barrage - bolstering other Israel's military's comments they will launch a "significant response".
“This launch of so many missiles, cruise missiles and drones into Israeli territory will be met with a response," he said in the clearest confirmation that Israel was plotting a revenge strike.
Israeli PM Benjamin Netanyahu met with his war cabinet for a second time yesterday after already hinting that plans had been drawn up - without specifying their nature or scale.
However, a leak from the PM's crunch talks suggest Israel is planning a "painful" strike that does not cause casualties.
Netanyahu has reportedly asked the IDF to compile a list of targets that Israel could choose to hit that the US would not object to.
Israel had said it reserves the right to strike Iran "at a manner and time" of its own choosing and told the UN that Iran "crossed every red line" in its attack.
But the question on everyone's lips is how will Israel choose to respond.
The Sun also told of the five major ways Israel may choose to respond - from fighter jet blitz on Tehran's nuclear facilities to a submarine strike or large-scale cyberattacks.
WEAPONS expert Colonel Hamish de-Bretton Gordon told The Sun that Iran was likely threatening a nuclear, chemical or biological attack.
But how likely would Tehran be to act on those threats or even be able to pull that kind of attack off?
A NUCLEAR STRIKE
De-Bretton Gordon said: "When the Iranians say they have a new weapon that nobody has seen before, people immediately think it's nuclear.
"We know they've been trying to enrich uranium. We think they're about 80 at the moment, and you need 90 plus to make a viable nuclear weapon."
With that knowledge, "I think it is pretty certain that at the moment the Iranians don't have a viable nuclear device."
A DIRTY BOMB
Instead, he suggested they could use its missiles capable of delivering a nuclear warhead refitted with a dirty bomb - an explosion that scatters radioactive material.
However, the last few days, the expert said, “have proved Iran is unable to deliver a missile or a drone to Israel" so they "cannot guarantee it" they could deliver a dirty bomb.
Iran could, however, deliver fissile material to Tel Aviv or Jerusalem to let off a dirty bomb. "But this is very difficult. One thing about nuclear material is, it's relatively easy to detect."
CHEMICAL WEAPONS
Iran could be thinking about a potential chemical weapon. But Colonel de-Bretton Gordon said: "We haven't seen the Iranians use chemical weapons for a long time since the Iraq War from 1984 to 88.
"But the fact that we're seeing Russia using chemical weapons in the form of CS gas in Ukraine at the moment with success could mean that is a potential for Iran.
"But I then how do they do it? How would they deliver it?"
The expert said missiles and drones are now clearly out of the question and Iran's fleet of fighter jets "are highly unlikely to get close enough to Israel to be able to do it".
A BIG BLUFF
De Bretton-Gordon argued Iran is "desperately concerned" about Israel's reaction to their drone and missile barrage and looking for a way out by threatening escalation.
He said: "The Iranians seem to be very much on the back foot, saying, 'It's all over. Now let's draw a line under it'.
"I can't see that the Iranians have a viable chemical, biological, or nuclear weapon with which to attack Israel with."
As Iran braces for Israel's "significant" response, world leaders have pushed for calm to avoid further escalation.
PM Rishi Sunak has demanded Israel show restraint in response to Iran's onslaught, calling out Tehran for its “reckless and dangerous escalation” that is the work of a “despotic regime”.
A joint statement by the G7 also urged for caution, fearing an "uncontrollable" war in the region.
UK foreign minister David Cameron said this morning that Iran's attack was significant and Israel has "every right to respond".
While he urged caution to "avoid escalation", he said Israel would "make their own decisions".
The IDF announced on Sunday night they had approved "both offensive and defensive actions" - but did not reveal further detail.
UN Secretary General Antonio Guterres told an emergency Security Council meeting on Sunday: "The Middle East is on the brink.
"The people of the region are confronting a real danger of a devastating full-scale conflict. Now is the time to defuse and de-escalate."
IRAN, a formidable and dangerous world power, is home to a number of nuclear sites.
It is thought to have active nuclear sites, research reactors and uranium mines.
Arak plant - satellite pictures of this plant near the Iranian town of Arak surfaced over 20 years ago.
It contains a heavy-water reactor with plutonium that can be used for nuclear bombs.
Bushehr nuclear power station - this power plant is a combination of Russian and German engineering.
It's nuclear reactor is operating at 100% power and the site is home to enriched uranium, used for nuclear bombs.
Gachin uranium mine - home to uranium ore concentrate, or yellowcake, which can be transformed into enriched uranium ready for nuke bomb assembling.
Isfahan conversion plant - yellowcake is converted here into three dangerous substances.
Hexafluoride gase used in the enrichment process, uranium oxide used to fuel reactors and metal used in the cores of nuclear bombs.
Natanz uranium enrichment plant - this is Iran's largest enrichment base.
It's made up of three underground buildings and is closely watched by the international community.
Parchin military site - south of Tehran, this site is focused on research and the production of ammo, rockets and explosives.
Concerns have been raised that it is also used as part of Iran's nuclear weapon development.
Qom uranium enrichment plant - a heavily fortified and initially secret facility where Iran carries out uranium enrichment.
