Iran fired a volley of missiles on Wednesday (January 8th) at Iraqi bases housing US and other foreign troops deployed as part of the international coalition fighting the "Islamic State of Iraq and Syria" (ISIS).
Launched for the first time by forces inside Iran instead of by proxy, the attack marked a new turn in the intensifying confrontation between the US and Iran.
"Iran launched more than a dozen ballistic missiles against US military and coalition forces in Iraq," the Pentagon said.
"It is clear that these missiles were launched from Iran and targeted at least two Iraqi military bases hosting US military and coalition personnel," it added.
The missiles targeted the sprawling Ain al-Assad airbase in western Iraq and a base in Erbil, both housing US and international coalition troops.
Iran's supreme leader Ali Khamenei, who has the final say in all matters of state, said it was a "slap in the face" for the US but that revenge was yet to come.
Facilities on 'high alert'
The Pentagon said the facilities had been on "high alert" after days of steadily mounting tension.
The office of Iraqi Prime Minister Adel Abdul Mahdi said it had received "an official verbal message" from Iran informing it a missile attack on US forces was imminent.
A spokesman for the prime minister said his office was simultaneously contacted by Washington as the missiles rained down.
"Iraq rejects any violation of its sovereignty and attacks on its territory," the statement said.
Iraq's military said it sustained no casualties in 22 missile strikes, most of them hitting Ain al-Assad.
US President Donald Trump said initial casualty assessments indicated "all is well".
France too said it sustained no casualties. But British Foreign Secretary Dominic Raab voiced concern about "reports of casualties".
"We condemn this attack on Iraqi military bases hosting coalition -- including British -- forces," Raab said. "We are concerned by reports of casualties and use of ballistic missiles."
The Norwegian military said international coalition troops were warned of the attack in advance through intelligence channels.
Iran claims missile strikes
Iran's Islamic Revolutionary Guard Corps (IRGC) said Ain al-Assad was hit with dozens of missiles in response to Friday's US strike in Baghdad that killed IRGC-Quds Force commander Qassem Soleimani.
It warned any US counter-attack would be met with an even "more crushing response" and threatened to strike Israel and US "allied governments".
"An important incident has happened. The question of revenge is another issue," Khamenei said in a speech broadcast live on state television in which he appeared to hint that more would come.
"Military actions in this form are not sufficient for that issue," he said, calling for an end to the US presence in the region.
Iran's Foreign Minister Mohammad Javad Zarif had seemed to indicate the missile strikes were over for now.
"Iran took and concluded proportionate measures in self-defence," Zarif said.
The brazenness of the strike was highly unusual for Iran, which has tended to disguise attacks on US interests or troops through its use of proxy forces.
This time, conventional, rather than guerrilla-style weapons were used and responsibility was rapidly claimed.
"It is a major escalation. Ballistic missiles openly launched from Iran onto American targets is a new phase," said Phillip Smyth, an expert on Shia militias.