Iran promised vengeance after a US air strike in Baghdad yesterday killed Qassem Soleimani, Tehran’s most prominent military commander and the architect of its growing influence in the Middle East.

Soleimani, a 62-year-old general who headed the elite Quds Force, was regarded as the second most powerful figure in Iran after Supreme Leader Ayatollah Ali Khamenei.

The overnight attack, authorised by President Donald Trump, was a dramatic escalation in a “shadow war” in the Middle East between Iran and the United States and its allies, principally Israel and Saudi Arabia.

US Secretary of State Mike Pompeo said the strike aimed to disrupt an “imminent attack” that would have endangered Americans in the Middle East. Democratic critics said the Republican president had raised the risk of more violence in a dangerous region.

Pompeo, in interviews on Fox News and CNN, declined to discuss many details of the alleged threat but said it was “an intelligence based assessment” that drove the decision to target Soleimani.

In a tweet, Trump said Soleimani had “killed or badly wounded thousands of Americans over an extended period of time, and was plotting to kill many more”, but did not elaborate.

The attack also killed pro-Iran Iraqi militia Hashed al-Shaabi’s deputy chief Abu Mahdi al-Muhandis.

The attack followed a sharp increase in US-Iranian hostilities last week when pro-Iranian militiamen attacked the US embassy in Iraq following a deadly US air raid on the Kataib Hezbollah militia, founded by Muhandis.

Khamenei said “harsh revenge” awaited the “criminals” who killed Soleimani and said his death would redouble resistance against the United States and Israel. He called for three days of national mourning starting from today and appointed Soleimani’s deputy, Brigadier General Esmail Ghaani, to replace him as Quds Force head.

“America should know that its criminal attack on General Soleimani has been the country’s biggest mistake in west Asia, and America will not avoid the consequences of this wrong calculation easily,” the Iranian Supreme National Security Council said in a statement.

“These criminals will face severe vengeance... in the right place and time,” it added.

US officials said Soleimani was killed in a drone strike. Iran said he died in an attack by US helicopters.

Tens of thousands of angry Iranians took to the streets of Tehran chanting “Death to America” and holding up posters of Soleimani, who was widely admired in the Islamic republic.

The US embassy in Baghdad urged all American citizens to leave Iraq “immediately” and US nationals working at southern oil fields were being evacuated, Iraq’s petrol ministry said.

Amid rising threats to American forces in the region, US officials yesterday said that Pentagon was sending up to 3,500 additional troops to the Middle East from the 82nd Airborne Division as a precaution.

The officials, speaking on condition of anonymity, said the troops would be joining the roughly 750 forces that were sent to Kuwait earlier this week.

Since May, the United States has already dispatched about 14,000 additional troops to the Middle East.

Earlier yesterday, a precision drone strike, as claimed by US, struck two cars belonging to Iraq’s Hashed al-Shaabi, a paramilitary force with close ties to Iran, as they drove away from Baghdad International Airport.

Hours later, Iran’s Revolutionary Guard Corps announced Soleimani “was martyred in an attack by America”. It said five Guards were killed in total as well as five members of the Hashed.

Both Soleimani and Abu Mahdi al-Muhandis were targeted by US sanctions.

Iraq’s parliament is set to hold an emergency meeting today where the presence of US forces in the country is expected to be discussed. A leading Hashed member, Hadi al-Ameri, urged lawmakers “to take a bold decision to oust foreign troops from Iraq, because their presence has become a threat for Iraqis”.

Some 5,200 US troops are stationed across the country, and a US defence official told AFP that some additional forces had arrived in recent hours to boost security at the American embassy.

Iran’s Foreign Minister Mohammad Javad Zarif slammed the US strike as “extremely dangerous and a foolish escalation,” as Khamenei declared three days of mourning.

Iraqi Prime Minister Adel Abdel Mahdi said the strike was a “flagrant violation” of a security accord with the US, warning it would “spark a devastating war in Iraq”.

And Iraqi President Barham Saleh called for “restraint” -- an appeal echoed by alarmed foreign governments. Israel put its army on high alert and US allies in Europe including Britain, France and Germany voiced concerns about an escalation in tensions.

UN Secretary General Antonio Guterres called for de-escalation in the Gulf, saying: “The world cannot afford another war in the Gulf.”

But paramilitary figures in Iraq including US-blacklisted Qais al-Khazali and militiaman-turned-politician Moqtada Sadr called on their fighters to “be ready”.

And in Lebanon, the leader of the Tehran-backed Hezbollah, Hassan Nasrallah, warned of “punishment for these criminal assassins.”

As fears of a regional conflagration grew, Yemen’s pro-Tehran Huthi rebels -- who have launched a string of missile attacks on Iran’s regional rival Saudi Arabia -- called for “swift reprisals”.

But there were daring celebrations in Baghdad’s Tahrir Square, the epicentre of a three-month-old protest movement that has slammed the Iraqi government as corrupt and beholden to Tehran.

“Oh Qasem Soleimani, this is a divine victory,” demonstrators chanted as some danced in the streets.

And Israeli Prime Minister Benjamin Netanyahu praised Trump “for acting swiftly, forcefully and decisively,” as Israeli tanks deployed along the occupied Golan Heights in fear of reprisal attacks.

Trump critics called the operation reckless.

“President Trump just tossed a stick of dynamite into a tinderbox,” said former Vice President Joe Biden, a contender in this year’s US presidential election.

As leader of the Quds Force, the foreign arm of the Guards, Soleimani had a key role in fighting in Syria and Iraq.

Over two decades he was at the forefront of projecting the Islamic Republic’s military influence across the Middle East, acquiring celebrity status at home and abroad.

Analysts said the strike -- which sent world oil prices soaring over concern about disruption to Middle East supplies-- would be a game-changer in the tensions between Iran and the US.

Phillip Smyth, a US-based specialist in Shiite armed groups, described the killing as “the most major decapitation strike that the US has ever pulled off”.

He told AFP it would have “bigger” ramifications than the 2011 US operation that killed al-Qaeda chief Osama bin Laden and the 2019 American raid that killed Islamic State group Abu Bakr al-Baghdadi.

Ties between the US and Iran have deteriorated markedly since Washington abandoned a landmark nuclear deal with Tehran in 2018 and reimposed crippling sanctions.

On Tuesday, a mob of Hashed supporters surrounded the US embassy, angered by American air strikes that killed 25 fighters from the network’s hardline Iran-backed Kataeb Hezbollah faction.

The US had acted in response to a rocket attack days earlier that killed an American contractor working in Iraq on Friday.

Trump had blamed Iran for the embassy siege and rocket attacks, saying: “They will pay a very BIG PRICE! This is not a Warning, it is a Threat.”