The United States military killed General Qasem Soleimani, the powerful commander of Iran's Revolutionary Guards, in a drone strike in Iraq on Friday to protect American personnel abroad, dramatically escalating hostilities between the arch-rivals and spiking tensions in the already volatile Persian Gulf region.
Gen Soleimani, the head of Iran's elite al-Quds force and architect of its regional security apparatus, was killed when a drone fired missiles into a convoy that was leaving the Baghdad International Airport early on Friday.
The strike also killed the deputy chief of Iraq's powerful Hashed al-Shaabi paramilitary force and some local Iran-backed militias.
Gen Soleimani, 62, was widely seen as the second most powerful figure in Iran behind the Ayatollah Khamenei.
His Quds Force, an elite unit of the Iranian Revolutionary Guards, reported directly to the ayatollah and he was hailed as a heroic national figure.
The Pentagon confirmed the death of Soleimani in the air strike, saying the military action was carried out at the direction of President Donald Trump.
"At the direction of the president, the US military has taken decisive defensive action to protect US personnel abroad by killing Qasem Soleimani, the head of the Iranian Revolutionary Guard Corps-Quds Force, a US-designated Foreign Terrorist Organisation," the Pentagon said in a statement.
Following Soleimani's killing, Trump, on vacation in Florida, initially tweeted an image of the US flag.
Hours later, he tweeted again. "Iran never won a war, but never lost a negotiation!" he wrote, in an apparent slight against the nuclear deal his predecessor Barack Obama negotiated with Tehran.
Later in series of tweets, Trump said that General Soleimani should have been eliminated many years ago as the powerful commander of Iran's Revolutionary Guards killed and wounded thousands of Americans and was plotting to kill many more
"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. 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!," Trump tweeted.
The strike comes days after Trump threatened Tehran after Iraqi supporters of pro-Iranian regime factions laid siege to the US embassy in Baghdad, following deadly American air strikes on a hardline Hashed faction.
Gen Soleimani and officials from Iran-backed militias were leaving Baghdad airport in two cars when they were hit by a US drone strike near a cargo area.
He had reportedly flown in from Lebanon or Syria. Several missiles struck the convoy and at least six people are believed to have died, according to media reports from Baghdad.
The Pentagon alleged that the strike was aimed at deterring future Iranian attack plans.
"General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region. General Soleimani and his Quds Force were responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more," it said.
The Pentagon said that Soleimani had "orchestrated" attacks on coalition bases in Iraq over the last several months - including the attack on December 27 - culminating in the death and wounding of additional American and Iraqi personnel.
"General Soleimani also approved the attacks on the US embassy in Baghdad that took place this week," it said.
"The US will continue to take all necessary action to protect our people and our interests wherever they are around the world,” it said.
In Tehran, Iran's Supreme Leader Ayatollah Ali Khamenei said "severe revenge awaits the criminals" behind the attack. He also announced three days of national mourning.
"For years it was his wish to become a martyr, and finally God granted him his highest office", Khamenei said.
President Hasan Rouhani, reacting to Soleimani's killing, said it had "redoubled the determination of the nation of Iran and other free nations to stand against America's bullying and defend Islamic values".
Meanwhile, global oil prices have soared by more than four per cent in the wake of the attack.
The news of Soleimani's killing generated different reactions in Washington along party lines with Republicans heaping praise on Trump and Democrats expressing concerns about the legality and consequences of the strike.
"I appreciate President @realDonaldTrump's bold action against Iranian aggression," Senator Lindsey Graham of South Carolina, a fierce Trump ally, tweeted. "To the Iranian government: if you want more, you will get more."
Trump's decision was supported by his former Cabinet colleague, Indian- American Nikki Haley, the former US Ambassador to the United Nations.
"Qasem 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,” she tweeted.
Senator Marco Rubio backed Trump's action in a tweet. “They chose to ignore these warnings because they believed @POTUS was constrained from acting by our domestic political divisions. They badly miscalculated,” he said.
Senator Bernie Sanders, who is also running for president in the Democratic primary, called it a "dangerous escalation" that brings the US "closer to another disastrous war in the Middle East that could cost countless lives and trillions more dollars."
"Trump promised to end endless wars, but this action puts us on the path to another one,” he said.
House Speaker and top Democrat Nancy Pelosi warned the US could not "put the lives of American service members, diplomats and others further at risk by engaging in provocative and disproportionate actions."
Ties between the US and Iran have deteriorated since Washington pulled out of the landmark nuclear deal with Tehran in 2018.
The US then reimposed crippling sanctions on Iran, aiming to choke off its oil exports.