"We urge Iran not to repeat these reckless and risky attacks, and instead to pursue urgent de-escalation".
Iran's Islamic Revolutionary Guard Corps (IRGC) said Wednesday that it targeted Ain al-Asad airbase in Iraq, a facility jointly operated by USA and Iraqi forces, with "tens of missiles". Iraq said 22 missiles were fired.
The attacks came after pro-Tehran factions in Iraq had vowed to "respond" to a U.S. drone strike that killed Iranian general Qasem Soleimani in Baghdad last week. "No Americans were harmed in last night's attack by the Iranian regime".
The White House press secretary said Donald Trump "has been informed and is monitoring the situation closely and consulting with his national security team".
"All is well!", Trump said Twitter.
Videos on social media are showing Iranian ballistic missiles hitting two airbases in Iraq used by American and coalition troops.
The attack comes days after the United States killed top Iranian General Qasem Soleimani in an airstrike in the Iraqi capital of Baghdad.
Germany, Denmark, Norway and Poland said none of their troops in Iraq were hurt.
Mr Trump tweeted all was well and said casualties and damage were being assessed.
It said the department is now working on initial damage assessments, and taking necessary measures to protect and defend United States personnel, partners and allies in the region.
More than 5,000 USA troops remain in Iraq along with other foreign forces in coalition that has trained and backed Iraqi forces against the threat of Islamic State militants.
State television quoted the head of Iran's emergency medical services, Pirhossein Koulivand, saying there had been a deadly stampede.
"Closely monitoring the situation following bombings targeting USA troops in Iraq", Pelosi said.