Iran has vowed "harsh retaliation" for a US airstrike near Baghdad's airport that killed Iran's top general and the architect of its interventions across the Middle East, as tensions soared in the wake of the targeted killing.

And, overnight NZT, the US embassy in Baghdad told all Americans to "leave Iraq immediately" - going by airline where possible and "failing that, to other countries via land".

US President Donald Trump retweeted that warning.

The killing of General Qassem Soleimani, the head of Iran's elite Quds Force, marks a major escalation in the standoff between Washington and Iran, which has careened from one crisis to another since Trump withdrew from the 2015 nuclear deal and imposed crippling sanctions.

Advertisement

Overnight NZT, Trump issued his first words on the killing of Qassem Soleimani, claiming the Iranian general killed thousands of Americans and should have been "taken out many years ago".

"General Qassem Soleimani has killed or badly wounded thousands of Americans over an extended period of time, and was plotting to kill many more...but got caught! He was directly and indirectly responsible for the death of millions of people, including the recent large number of PROTESTERS killed in Iran itself," the president tweeted.

"While Iran will never be able to properly admit it, Soleimani was both hated and feared within the country. They are not nearly as saddened as the leaders will let the outside world believe. He should have been taken out many years ago!" he added.

Trump is in Mar-a-Lago for the holiday season and is not going to his golf course Friday, which is where he has spent the majority of his days while in Florida.

Iran's Supreme Leader Ayatollah Ali Khamenei warned that a "harsh retaliation is waiting" for the US after the airstrike, calling Soleimani the "international face of resistance".

Khamenei declared three days of public mourning for the general's death. Iran also summoned the Swiss charges d'affaires, who represents US interests in Tehran, to protest the killing.

The killing, and any forceful retaliation by Iran, could ignite a conflict that engulfs the whole region, endangering US troops in Iraq, Syria and beyond. Over the past two decades Soleimani had assembled a network of powerful and heavily armed allies stretching all the way to southern Lebanon, on Israel's doorstep.

The Defence Department said it killed Soleimani because he "was actively developing plans to attack American diplomats and service members in Iraq and throughout the region". It also accused Soleimani of approving the orchestrated violent protests at the US Embassy in Baghdad earlier this week. Iranian state television called Trump's order to kill Soleimani "the biggest miscalculation by the US" since World War II.

Advertisement

"The people of the region will no longer allow Americans to stay," it said. The airport strike also killed Abu Mahdi al-Muhandis, deputy commander of Iran-backed militias in Iraq known as the Popular Mobilisation Forces, and five others, including the PMF's airport protocol officer, Mohammed Reda, Iraqi officials said.

Trump was vacationing on his estate in Palm Beach, Florida, but sent out a tweet of an American flag.

The dramatic attack comes at the start of a year in which Trump faces both a Senate trial following his impeachment by the Congress and a re-election campaign. It marks a potential turning point in the Middle East and represents a drastic change for American policy toward Iran after months of tensions. Tehran shot down a US military surveillance drone and seized oil tankers last year.

The US also blames Iran for a series of other attacks targeting tankers, as well as a September assault on Saudi Arabia's oil industry that temporarily halved its production.

The tensions are rooted in Trump's decision in May 2018 to withdraw the US from Iran's nuclear deal with world powers, struck under his predecessor, Barack Obama. The 62-year-old Soleimani was the target of today's US attack, which was conducted by an armed American drone, according to a US official. His vehicle was struck on an access road near the Baghdad airport.

A senior Iraqi security official said the airstrike took place near the cargo area after Soleimani left his plane and joined al-Muhandis and others in a car.

Advertisement

The official said the plane had arrived from either Lebanon or Syria. PMF officials said the bodies of Suleimani and al-Muhandis were torn to pieces. A senior politician said Soleimani's body was identified by the ring he wore. The officials spoke on condition of anonymity because they were not authorised to give statements to the media. It's unclear what legal authority the US relied on to carry out the attack. American presidents claim broad authority to act without the approval of the Congress when US personnel or interests are facing an imminent threat.

The Pentagon did not provide evidence to back up its assertion that Soleimani was planning new attacks against Americans.

House Speaker Nancy Pelosi said the "highest priority" was to protect American lives and interests, but that "we cannot put the lives of American service members, diplomats and others further at risk by engaging in provocative and disproportionate actions".

"Tonight's airstrike risks provoking further dangerous escalation of violence. America – and the world – cannot afford to have tensions escalate to the point of no return," she said in a statement.

She said Congress was not consulted on the strike and demanded it be "immediately" briefed on the situation and the next steps.

Democratic presidential candidate Joe Biden said Trump had "tossed a stick of dynamite into a tinderbox," and like other Democratic White House hopefuls criticised Trump's order, saying it could leave the US "on the brink of a major conflict across the Middle East". But Trump allies were quick to praise the action.

Advertisement

"To the Iranian government: if you want more, you will get more," tweeted South Carolina Senator Lindsey Graham.

For Iran, the killing represents the loss of a cultural icon who represented national pride and resilience while facing US sanctions. While careful to avoid involving himself in politics, Soleimani's profile rose sharply as US and Israeli officials blamed him for Iranian proxy attacks abroad.

While Iran's conventional military has suffered under 40 years of American sanctions, the Guard has built up a ballistic missile programme. It also can strike asymmetrically in the region through forces like Lebanon's Hezbollah and Yemen's Houthi rebels. The US has long blamed Iran for car bombings and kidnappings it never claimed.

As the head of the Quds, or Jerusalem, Force of Iran's paramilitary Revolutionary Guard, Soleimani led all of its expeditionary forces and frequently shuttled between Iraq, Lebanon and Syria. Quds Force members have deployed into Syria's long war to support President Bashar Assad, as well as into Iraq in the wake of the 2003 US invasion that toppled dictator Saddam Hussein, a longtime foe of Tehran.

Soleimani rose to even greater prominence by advising forces fighting the Islamic State group in Iraq and in Syria. US officials say the Guard under Soleimani taught Iraqi militants how to manufacture and use especially deadly roadside bombs against US troops after the invasion of Iraq. Iran has denied that. Soleimani himself remains popular among many Iranians, who see him as a selfless hero fighting Iran's enemies abroad.

Soleimani had been rumoured dead several times, including in a 2006 airplane crash that killed other military officials in northwestern Iran and following a 2012 bombing in Damascus that killed top aides of Assad. Rumours circulated in November 2015 that Soleimani was killed or seriously wounded leading forces loyal to Assad as they fought around Syria's Aleppo.

Advertisement

Soleimani's killing follows the New Year's Eve attack by Iran-backed militias on the US Embassy in Baghdad. The two-day embassy attack prompted Trump to order about 750 US troops deployed to the Middle East. No one was killed or wounded in the attack, which appeared to be mainly a show of force.

It prompted Secretary of State Mike Pompeo to postpone his trip to Ukraine and four other countries "to continue monitoring the ongoing situation in Iraq and ensure the safety and security of Americans in the Middle East," the State Department said. The breach at the embassy followed US airstrikes Sunday that killed 25 fighters of Kataeb Hezbollah, an Iran-backed militia operating in Iraq and Syria. The US military said the strikes were in retaliation for last week's killing of an American contractor in a rocket attack on an Iraqi military base that the US blamed on the militia.

US officials have suggested they were prepared to engage in further retaliatory attacks in Iraq.

"The game has changed," Defence Secretary Mark Esper said today, telling reporters that violent acts by Iran-backed Shiite militias in Iraq would be met with US military force.

- AP