BAGHDAD (AP) — Iran vowed “harsh retaliation” for a US airstrike near Baghdad’s airport that killed a top Iranian general who had been the architect of its interventions across the Middle East, as tensions soared in the wake of the targeted killing.

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

The United States urged American citizens to leave Iraq “immediately” following Thursday night’s airstrike at Baghdad’s international airport that Iran’s State TV said killed Soleimani and nine others. The State Department said the embassy in Baghdad, which was attacked by Iran-backed militiamen and their supporters earlier this week, is closed and all consular services have been suspended.

Around 5,200 American troops are based in Iraq to train Iraqi forces and help in the fight against Islamic State group militants. US embassies also issued a security alert for Americans in Lebanon, Bahrain Kuwait and Nigeria.

Iran’s Supreme Leader Ayatollah Ali Khamenei warned that “harsh retaliation is waiting” for the US after the airstrike, calling Soleimani the “international face of resistance”. Khamenei declared three days of public mourning and appointed Major General Esmail Ghaani, Soleimani’s deputy, to replace him as head of the Quds Force.

Iranian President Hassan Rouhani called the killing a “heinous crime” and vowed his country would “take revenge”.

Thousands of worshippers in the Iranian capital Tehran took to the streets yesterday after Muslim prayers to condemn the killing, waving posters of Soleimani and chanting “Death to deceitful America.”

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

However, the attack may act as a deterrent for Iran and its allies to delay or restrain any potential response. Oil prices surged on news of the airstrike and markets were mixed.

The killing promised to further strain relations with Iraq’s Government, which is allied with both Washington and Tehran and has been deeply worried about becoming a battleground in their rivalry. Iraqi politicians close to Iran called for the country to order US forces out.

The Defence Department said it killed the 62-year-old 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.

The strike, on an access road near Baghdad’s airport, was carried out by an American drone, according to a US official.

Soleimani had just disembarked from a plane arriving from either Syria or Lebanon, a senior Iraqi security official said. The blast tore his body to pieces along with that of Abu Mahdi al-Muhandis, deputy commander of the Iranian-backed militias in Iraq known as the Popular Mobilisation Forces. A senior politician said Soleimani’s body was identified by the ring he wore. Iran’s State TV said yesterday that 10 people were killed in the airstrike, including five Revolutionary Guard members and Soleimani’s son-in-law, whom he did not identify.

The officials spoke on condition of anonymity because they were not authorised to talk to reporters.

The attack comes at the start of a year in which Trump faces both a Senate trial following his impeachment by 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.

The tensions are rooted in 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.

Since then, Tehran shot down a US military surveillance drone and seized oil tankers. The US also blames Iran for other attacks targeting tankers and a September assault on Saudi Arabia’s oil industry that temporarily halved its production.

Supporters of the strike said it restored US deterrence power against Iran, and Trump allies were quick to praise the action. “To the Iranian government: if you want more, you will get more,” South Carolina Senator Lindsey Graham tweeted.

“Hope this is the first step to regime change in Tehran,” Trump’s former National Security Adviser, John Bolton wrote in a tweet.

Others, including Democratic White House hopefuls, criticised Trump’s order. Democratic presidential candidate Joe Biden said Trump had “tossed a stick of dynamite into a tinderbox,” saying it could leave the US “on the brink of a major conflict across the Middle East”.

Trump, who is vacationing at his private club in Palm Beach, Florida, said in a tweet yesterday that the airstrike was ordered because Soleimani was “plotting to kill” many Americans. “He should have been taken out many years ago!” Trump tweeted.