Iran has carried out a ballistic missile attack on air bases housing US forces in Iraq, in retaliation for the US killing of General Qasem Soleimani.
More than a dozen missiles launched from Iran struck two air bases in Irbil and Al Asad, west of Baghdad.
It is unclear if there have been any casualties.
The initial response from Washington has been muted. President Trump tweeted that all was well and said casualties and damage were being assessed.
Two Iraqi bases housing US and coalition troops were targeted - one at Al Asad and one in Irbil at about 2:00am local time (10.30pm GMT), just hours after the burial of Soleimani.
The Al Asad airbase - located in the Anbar province of western Iraq - was hit by at least six missiles.
Iran's Supreme Leader Ayatollah Khamenei said the attack was "a slap in the face" for the US.
"When it comes to confrontation, military action of this kind is not enough. What is important is that the corrupt presence of the United States should come to an end," he said.
Is this the end of the escalation?
This is the most direct assault by Iran on the US since the seizing of the US embassy in Tehran in 1979.
Iran's Revolutionary Guards said the attack was in retaliation for the death of Soleimani on Friday - killed in a missile strike outside Baghdad airport on the orders of President Trump.
"We are warning all American allies, who gave their bases to its terrorist army, that any territory that is the starting point of aggressive acts against Iran will be targeted," a statement said.
The chief of staff of Iran's regular military, Maj Gen Mohammad Baqeri, said the missile attack showed just a "small part" of the capabilities of the Iranian armed forces.
But Iranian Foreign Minister Mohammad Javad Zarif issued a statement on Twitter, claiming the attack was self-defence and denied seeking to escalate the situation into war.
The BBC's Middle East editor Jeremy Bowen in Baghdad says the tweets appear to suggest that Iran wishes to draw a line under its retaliation for the assassination of Soleimani and is putting the onus on the US as to whether the situation escalates.