US forces have killed a top Iranian general in a drone airstrike on Baghdad airport - an attack that marks a dramatic escalation of tensions with Tehran.
Iran immediately threatened a "crushing revenge" for the assassination in Iraq of Major General Qassem Soleimani, the head of Iran's elite Quds Force and spearhead of Iran's spreading military influence in the Middle East.
The Pentagon confirmed US forces had killed the general, a revered figure in the region, on Friday.
It said Maj Gen Soleimani, 62, had "orchestrated" attacks on coalition bases in Iraq over the past few months and approved the "attacks" on the US Embassy in Baghdad earlier this week.
"This strike was aimed at deterring future Iranian attack plans," the Pentagon said in a statement, adding that the US would continue to take necessary action to protect Americans and interests around the world.
Abu Mahdi al Muhandis, the deputy commander of Iran-backed militias known as the Popular Mobilisation Forces (PMF) and an adviser to Maj Gen Soleimani, was also killed during the strike.
The Pentagon said the strike was carried out "at the direction" of President Donald Trump, who tweeted an image of the American flag several hours after the attack.
The US embassy in Baghdad has urged American citizens to depart Iraq immediately "via airline while possible, and failing that, to other countries via land".
Iranian Defence Minister Amir Hatami said: "A crushing revenge will be taken for Soleimani's unjust assassination ... We will take revenge from all those involved and responsible for his assassination".
Iranian Foreign Minister Mohammad Javad Zarif said in a post on Twitter: "The US act of international terrorism, targeting & assassinating General Soleimani... is extremely dangerous & a foolish escalation. The US bears responsibility for all consequences of its rogue adventurism."
Iran's Supreme Leader Ayatollah Ali Khamenei also warned that a "harsh retaliation" is waiting for the US.
The rising tension between the US and Iran helped push the cost of Brent crude oil to $68 per barrel - a rise of 3%.
The airstrike was conducted by a US drone, and according to a US official, Maj Gen Soleimani's vehicle was struck on an access road near the airport.
A senior Iraqi security official said the strike took place near the cargo area after Maj Gen Soleimani left his plane to be greeted by Mr al Muhandis. The plane had arrived from either Lebanon or Syria.
An Iranian politician said Maj Gen Soleimani's body was identified by the ring he wore. An official from the PMF said they did not find the body of Mr al Muhandis.
It is unclear what legal authority the US relied on to carry out the attack. American presidents claim broad authority to act without congressional approval when US personnel or interests are facing an imminent threat.
The attack comes amid tensions with the US after the New Year's Eve attack by Iran-backed militias on the US Embassy in Baghdad.
The two-day embassy attack which ended on Wednesday prompted Mr Trump to order the deployment of around 750 US soldiers to the Middle East.
The breach at the embassy followed US airstrikes on Sunday that killed 25 fighters of the Iran-backed militia in Iraq, the Kataeb Hezbollah.
The US military said the Sunday 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.
Maj Gen Soleimani, who led the foreign arm of the Revolutionary Guards and had a key role in fighting in Syria and Iraq, acquired celebrity status at home and abroad.
He was instrumental in the spread of Iranian influence in the Middle East, which the US and Tehran's regional foes Saudi Arabia and Israel have struggled to keep in check.
As head of the Quds Force, he frequently shuttled between Iraq, Lebanon and Syria.
He had survived several assassination attempts against him by Western, Israeli and Arab agencies over the past two decades.
His Quds Force, tasked with carrying out operations beyond Iran's borders, shored up support for Syrian President Bashar al Assad when he looked close to defeat in the civil war and also helped militias defeat Islamic State in Iraq.
Sky News foreign affairs editor Deborah Haynes said: "It's hard to overstate the importance of Qassem Soleimani. He is someone who has been instrumental to Iranian foreign policy since the 2003 invasion of Iraq by the US and its allies.
"The taking out of this figure is a hugely bold move by the US.
"Iran will feel compelled to retaliate. They cannot let an act like this go without an answer. America will have taken that into consideration when it decided to take this move.
"President Trump said Iran would pay 'a big price' for the storming of the US embassy in Baghdad a couple of days ago. I don't think anyone would have imagined it would be such a big price - probably even the Iranians."
Former US ambassador to the United Nations Nikki Haley tweeted: "Qassem Soleimani was an arch terrorist with American blood on his hands. His demise should be applauded by all who seek peace and justice.
"Proud of President Trump for doing the strong and right thing."
