AMERICA is threatening to send 4,000 paratroopers to Kuwait after Donald Trump warned Iran will "pay a very big price" for the US embassy attack.

At least 500 troops are already being deployed after 6,000 pro-Iranian thugs stormed the embassy in Baghdad.

A Shia thug brandishes a US diplomatic crest looted from the embassy in Baghdad today Credit: Reuters

The ambassador and his staff were evacuated as the mob tried to smash their way into the main building Credit: Getty - Contributor

A huge plume of black smoke rises over the US embassy in Baghdad today Credit: AP:Associated Press

6 US marines were today deployed to reinforce the embassy from a base in Kuwait Credit: Reuters

Gunfire was heard and troops fired tear gas after the Shia militiamen chanted "death to America", smashed down the gates and set fire to a guard post.

The US Army's 82nd Airborne Division has ordered troops to prepare for deployment to the Middle East, Fox News reports.

It came after furious Trump warned Iran's government will be held "fully responsible" for the attack.

The US President tweeted: "The U.S. Embassy in Iraq is, & has been for hours, SAFE! Many of our great Warfighters, together with the most lethal military equipment in the world, was immediately rushed to the site.

"Iran will be held fully responsible for lives lost, or damage incurred, at any of our facilities. They will pay a very BIG PRICE! This is not a Warning, it is a Threat. Happy New Year!"

TRUMP BLAST

US soldiers could be seen taking up defensive positions on the roof and inside the main building embassy as a huge plume of smoke rose over the fortified Green Zone.

Iraqi officials confirmed the ambassador and diplomatic staff were safely evacuated.

According to the Washington Post, US diplomats and staffers inside the embassy were huddled in a fortified safe room.

US defence secretary Mark Esper said tonight he would send reinforcements to guard the embassy.

It was reported 100 Marines would be redeployed from elsewhere in the region to bolster defences and two Apaches choppers will fly over in a "show of force".

President Trump accused Tehran of being behind the attack, which came after funerals for Iran-backed paramilitary fighters killed in air strikes on Sunday.

He tweeted: "Iran killed an American contractor, wounding many. We strongly responded, and always will.

"Now Iran is orchestrating an attack on the US Embassy in Iraq.

"They will be held fully responsible. In addition, we expect Iraq to use its forces to protect the Embassy, and so notified!"

Today's violence sparked painful memories of the murder of the US ambassador to Libya in the Benghazi embassy siege by Islamist terrorists in 2012.

Donald Trump said Tehran was behind the attack Credit: Twitter

A member of the Hashd al-Shaabi paramilitary forces wearing a Gucci top poses in the US embassy compound Credit: Reuters

Hundreds of Iran-backed thugs stormed the US embassy in Baghdad in protest at air strikes Credit: AP:Associated Press

They smashed down gates and set fire to a guard post Credit: AP:Associated Press

The thugs waved flags of Iran-back militia groups after storming through an outer wall Credit: Rex Features

The mob began attacking the Baghdad compound after thousands marched in protest at US air strikes that killed 25 fighters from an Iran-backed militia in Iraq and Syria.

Protesters raised yellow flags belonging to the Kataeb Hezbollah armed group over the walls.

They also smashed security cameras and hurled water bottles and stones as they surged into the compound shouting “Down, Down, USA”, “Death to America”, and “Death to Israel”.

They went on to taunt embassy security guards, who retreated inside and remained behind the glass windows as marchers approached.

Some protesters sprayed graffiti on the wall and windows in red in support of the Kataeb Hezbollah militia, saying: “Closed in the name of the resistance.”

Iraqi special forces and riot squads were called in as reinforcements after US troops fired tear gas in an attempt to disperse the crowd.

US soldiers seen inside the embassy ready to take on the rioters if they got further into the compound Credit: Reuters

Heavy armour was also called in ready to quell the riot Credit: Getty - Contributor

Iraqi special forces were also called in to keep the mob at bay Credit: Reuters

The thugs surged inside the outer part of the heavily fortified embassy compound Credit: AP:Associated Press

6 Hashd al-Shaabi fighters set fire to a US Embassy wall in Baghdad after air strikes targeted Iran-backed militia Credit: Reuters

6 Protesters were heard shouting 'Down, Down, USA', 'Death to America', and 'Death to Israel' Credit: Reuters

Gunfire was heard as security forces used tear gas to disperse the mob Credit: Reuters

The US military carried out strikes on Sunday against the Iranian-backed Kataeb Hezbollah militia after last week's killing of an American contractor in a rocket attack on an Iraqi military base which was blamed on the group.

The US attack – the largest targeting an Iran-sanctioned militia in recent years – and the calls for revenge represent a new escalation in the proxy war playing out in the Middle East.

Secretary of State Mike Pompeo said the strikes send the message that the US will not tolerate actions by Iran that threaten American lives.

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The Iranian-backed Iraqi militia vowed on Monday to retaliate.

Thousands of Iraqis have been protesting at the Iranian presence in the country, but today it was the Shiite militia on the streets.

The protest began after mourners held funerals for those killed in a Baghdad neighbourhood, after which they marched to the heavily fortified Green Zone until they reached the sprawling US embassy compound.

Protesters tried to get inside the embassy Credit: Reuters

Shiite warlord Qais al-Khazali (centre) marches on the embassy in protest at US air strikes Credit: EPA

They marched on the embassy after funerals for some of those killed in US air strikes on Sunday Credit: AFP or licensors

6 The mob broke down the gate at the US embassy in Baghdad and stormed inside the compound Credit: Reuters

6 Hundreds of Iraqi thugs attempt to storm US Embassy in Baghdad following deadly air strikes Credit: Getty - Contributor