The United States has killed Iranian Major-General Qassem Soleimani, head of the elite Quds Force and architect of Iran's spreading military influence in the Middle East, in an air strike on Friday at Baghdad airport, the Pentagon and Iran say.
Top Iraqi militia commander Abu Mahdi al-Muhandis, an adviser to Soleimani, was also killed in the attack that was authorised by US President Donald Trump.
Soleimani's killing marks a dramatic escalation in the regional "shadow war" between Iran and the United States and its allies, principally Israel and Saudi Arabia, which could quickly ratchet up tit-for-tat attacks.
Despite the action, Secretary of State Mike Pompeo said The United States remains committed to de-escalation with Iran but is prepared to defend itself.
Pompeo, speaking in an interview on Fox News, said he could only confirm that Qassem Soleimani, the commander of Iran's elite Quds Force, had been killed in the strike.
And President Trump tweeted late on Friday morning: "Iran never won a war, but never lost a negotiation!"
Iran's Supreme Leader Ayatollah Ali Khamenei has vowed harsh revenge.
Iran has been locked in a long conflict with the United States that escalated sharply last week with an attack on the US embassy in Iraq by pro-Iranian militiamen following a US air raid on the Kataib Hezbollah militia, founded by Muhandis.
"At the direction of the president, the U.S. military has taken decisive defensive action to protect U.S. personnel abroad by killing Qassem Soleimani," the Pentagon said in a statement.
"This strike was aimed at deterring future Iranian attack plans," it added.
US officials, speaking on the condition of anonymity, said that Soleimani had been killed in a drone strike. Iran's Revolutionary Guards said he was killed in an attack by American helicopters.
Pictures showed burning debris on a road near the airport.
Oil prices were up nearly $US3 ($A4.30) on the news.
Khamenei said harsh revenge awaited the "criminals" who killed Soleimani and his death, though bitter, would double the motivation of the resistance against the United States and Israel.
But it could be difficult for Iran to plan and carry out the kind of sophisticated attacks that Soleimani was accused of masterminding during his over 20 years of projecting the Islamic Republic's military influence across the Middle East.
Iraqi Prime Minister Adel Abdul Mahdi condemned the "assassination" of Soleimani and al-Muhandis. The air strike on Baghdad airport is an act of aggression on Iraq and breach of its sovereignty that will lead to war in Iraq, the region, and the world, he said in a statement.
The strike also violated the conditions of US military presence in Iraq and should be met with legislation that safeguards Iraq's security and sovereignty, he added. He called on parliament to convene in an extraordinary session.
State television presenters wore black and broadcast footage of Soleimani peering through binoculars across a desert and greeting a soldier, and of Muhandis speaking to followers.
President Hassan Rouhani said the assassination would make Iran more decisive in its resistance to the United States while Iran's Revolutionary Guards said anti-US forces would exact revenge across the Muslim world.
Iraqi paramilitary groups said three rockets hit Baghdad International Airport, killing five members of Iraqi paramilitary groups and two "guests".
The rockets landed near the air cargo terminal, burning two vehicles, killing and injuring several people.
Trump, who is facing impeachment charges, made no immediate comment but posted a picture of the US flag on Twitter.
Israel's prime minister has welcomed the airstrike, insisting President Trump "deserves all the credit for acting swiftly, forcefully and decisively."
Benjamin Netanyahu on Friday said Gen Soleimani, "is responsible for the death of American citizens and many other innocent people. He was planning more such attacks."
Iraqi Shi'ite cleric Moqtada al-Sadr, who portrays himself a nationalist rejecting both Iranian and US influence, ordered his followers to be ready to defend Iraq and urged all sides to behave wisely.
The Syrian government of President Bashar al-Assad condemned was it called criminal US aggression.
Russia's Foreign Ministry has also condemned the action and said it will increase tensions throughout the Middle East.
© DPA 2020