DONALD Trump insisted the US bombed a top Iran general to "stop a war" - as the US fears revenge attacks in major cities.
The president ordered the hit on Qasem Soleimani - said to be Iran's second most powerful figure - after claims he was plotting against American diplomats in Iraq.
But there are serious concerns the execution could cause the outbreak of World War Three after Iran's supreme leader Ali Khamenei promised "harsh vengeance", "jihad" and "crushing revenge".
Trump tonight tried to restore calm as he spoke on camera for the first time since giving the airstrike order.
He said: "We took action last night to stop a war. We did not take action to start a war.
"Soleimani was plotting imminent and sinister attacks on American diplomats and military personnel, but we caught him in the act and terminated him.
"Under my leadership America's policy is unambiguous to terrorists who harm or intend to harm any American. We will find you. We will eliminate you.
"We will always protect our diplomats, service members, all Americans and our allies."
Trump went on to insist Soleimani should have been killed "long ago" - and claimed a "reign of terror" is now over.
He also said he is “ready and prepared” to take whatever action is necessary, adding: "The president added: "The world is a safer place without these monsters."
This morning's dramatic attack came months of tensions between the US and Iran in which Tehran shot down an American military surveillance drone and seized oil tankers.
Searches for World War Three today spiked on Google within hours of the airstrike and began trending on Twitter as the news broke.
And Trump deployed 3,500 troops to the Middle East in retaliation to threats by Iran vowing to "turn day into night".
REVENGE ATTACK FEARS
Major US cities - including New York and Los Angeles - say they have already ramped up security in the aftermath to prevent any revenge attacks.
New York City mayor Bill de Blasio tonight announced he would be protecting key locations from "any attempt by Iran or its terrorist allies to retaliate against the US".
He added: "We have to assume this action puts us in a de facto state of war.
"No one has to be reminded that New York City is the number one terror target in the United States. We have to recognise that this creates a whole series of dangerous possibilities for our city.
"We have plenty of knowledge of previous efforts by Iranian proxies to scout and target locations in New York City.
"Hezbollah and others have made it a point in recent years... We know there's been an effort to target and prepare to attack in New York City in the past."
SLEEPER CELLS
NYPD Commissioner Dermot Shea confirmed more uniformed officers would be patrolling the streets - some heavily armed - while the LAPD said they were monitoring developments.
There are fears the Iran-backed Hezbollah militant group may already have sleeper cells in the US ready to pounce.
The group - deemed a terrorist organisation by the US - could potentially have targets in its sights, a former CIA operations officer warned.
Sam Faddis said: "Based on what we know we must assume they do and that they can hit targets on US soil at anytime without warning."
Soleimani had landed at Baghdad Airport early this morning where he was met by Abu Mahdi al-Muhandis, deputy commander of the pro-Iran Popular Mobilization forces in Iraq.
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As the cars passed through a cargo area for an access road leading out of the airport, the vehicle was struck by at least two missiles by a US MQ9 Reaper drone which was being controlled remotely.
At least two missiles were fired at the vehicles - killing the general and others on board.
Footage showed the moment US drones assassinated the general at Baghdad Airport.
Soleimani could only be identified by the ring on his severed hand.
The Sun Says
THE world is a far better place without war criminal Qasem Soleimani.
He was the truly evil mastermind of the slaughter of countless innocents in the Middle East and had the blood of many British and US troops on his hands.
Naturally, there are worries that Donald Trump has lit the fuse for fresh violence. But Iran and its proxies unleash constant savagery already, until yesterday under Soleimani’s personal direction. He was the architect of horrors in multiple countries.
He will be mourned only by Iran’s Islamic fundamentalists and, of course, by Jeremy Corbyn and his hard-left anti-American nitwits.
But Foreign Secretary Dominic Raab’s reaction was mealy-mouthed too. Of course it would be good for both sides to “de-escalate”. True, “further conflict is in none of our interests”. Mr Raab might have added a full-throated condemnation of Soleimani, effectively the world’s No1 terrorist, whose victims outnumber those of Bin Laden or al-Baghdadi.
Yes, the US should have warned Britain of the drone strike, given the heightened danger now to our 900 troops in Iraq and Syria. But it had to act rapidly.
Iranian reprisals may be inevitable. But standing back hasn’t done the West much good. The mullahs at least now need to factor in a US President who’s more ruthless than the last.
Three days ago Ayatollah Khamenei taunted him over the storming of the US embassy in Baghdad. “You can’t do anything,” he sneered.
Trump’s put him straight there.