THE US hit targets in Syria and Iraq tonight — striking back after three of its soldiers were killed by a drone.
Officials said American missile strikes had hit more than 85 targets, including “command and control headquarters” and ammo dumps.
US Central Command said it targeted Iran’s Islamic Revolutionary Guard’s Quds Force and linked militia groups.
Syrian media said cities in the east of the country were hit.
Iraq said 16 people, including civilians, were killed and 25 wounded.
Iraqi media was reporting strikes in Anbar Province, western Iraq, a large area bordering Syria and Jordan.
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Iran itself was not attacked.
US President Joe Biden tonight said: “Let all those who might seek to do us harm know this: If you harm an American, we will respond.”
US Central Command said the strikes used more than 125 munitions, delivered by numerous aircraft, including long-range bombers.
Britain expressed support for the strikes and said the US had a "right to respond" to the attacks on American troops.
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A Government spokesperson said: "The UK and US are steadfast allies.
"We wouldn't comment on their operations, but we support their right to respond to attacks.
"We have long condemned Iran's destabilising activity throughout the region, including its political, financial and military support to a number of militant groups."
It came hours after the President joined grieving families to see the remains of the three Army reservists returned home.
They were killed in the attack on the Tower 22 base, in Jordan, last Sunday.
They were Sgt William Rivers, 46, Specialist Kennedy Sanders, 24, and Specialist Breonna Moffett, 23.
More than 40 servicemen and women were also injured. The outpost was hit by an Iranian-made drone piloted from Iraq, just six miles away.
The Islamic Resistance, an umbrella group of Iran-backed militias in the region, claimed responsibility.
It said it came in response to the US’ support for Israel.
Official sources earlier this week, revealed plans for the retaliatory strikes and said they would involve a blitz on Iranian people and facilities.
On Friday ahead of the anticipated blitz, the US warned Iraq.
The White House said "We did inform the Iraqi government prior to the strikes."
But Iraqi military condemned the strikes on militant sites inside the country as a violation of the country's freedoms and rights.
The bombshell scheme was leaked as US Defence Secretary Lloyd Austin decried the barrage of drone and rocket attacks recently carried out by Iran-backed militias on US forces in the Middle East.
He said on Thursday afternoon: "The president will not tolerate attacks on American troops and neither will I. Our teammates were killed by radical militants backed by Iran, operating in Syria and Iraq."
Mr Austin added that Iran-backed rebels had "tried to create even more turmoil" ever since terror group Hamas unleashed its terror on Israel on October 7, killing 1,200 people and taking 240 hostage.
He declared: "This is a dangerous moment in the Middle East.
"We will take all necessary actions to defend the United States, our interests, and our people.
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"We will respond when we choose, where we choose, and how we choose. That's what everyone here is focused on."
Iran is a vital backer of Hamas and many other terrorist groups across the Middle East, including the Houthi rebels in Yemen, who are behind recent attacks against ships in the Red Sea and the Gulf of Aden, and Hezbollah in Lebanon.
Who are the Houthis?
THE Houthi rebels are terrorising vessels and warships in the Red Sea - but who are they?
The Shia militant group, which now controls most of Yemen, spent over a decade being largely ignored by the world.
However, since the outbreak of the Israel-Gaza war they sprung from relative obscurity to hostage - turning one of the world's busiest
Their warped slogan is “Death to America, Death to Israel, curse the Jews and victory to Islam”.
Why are they attacking ships?
The rebel group has been launching relentless drone and missile attacks on any ships - including warships - they deem to be connected with Israel in solidarity with their ally Hamas.
The sea assaults have threatened to ignite a full-blown war in the Middle East as ripples from Israel's war in Gaza are felt across the region - with Iran suspected of stoking the chaos.
However, there have been frequent attacks on commercial vessels with little or no link to Israel - forcing global sea traffic to halt operations in the region and sending shipping prices soaring.
Houthi attacks in the Red Sea increased 50 per cent between November and December.
The rebel group's leaders have previously pledged the attacks will continue until Israel stops its devastating offensive inside Gaza - despite recent US and UK strikes on their military strongholds.