What happened during Iran's attack on a U.S. air base in Iraq?

What happened?

Iran's Islamic Revolutionary Guard Corps (IRGC) has said it started an attack on an air base in western Iraq hosting U.S. troops on Wednesday, according to state television.

"The brave soldiers of IRGC's aerospace unit have launched a successful attack with tens of ballistic missiles on al-Asad military base in the name of martyr Gen. Qasem Soleimani," the IRGC said in a statement.

At least 10 rockets have attacked Ain al-Asad air base which holds U.S. forces in Iraq, media reports have said.

"The fierce revenge by the Revolutionary Guards has begun," the statement added.

Sirens have been heard, and U.S. helicopters were flying over the air base with a total alert activated, according to media reports.

The Pentagon has responded to the attack. It confirmed in a statement that Iran launched more than a dozen ballistic missiles against the U.S. military, targeting two Iraqi bases at Ain al-Asad and Irbil which host U.S. military and coalition personnel, adding that the U.S. will take all necessary measures to protect and defend U.S. personnel, partners, and allies in the region.

The casualties or extent of the damage caused by the attack was not immediately clear as tension mounted between Washington and Tehran following the U.S. killing on Friday of Iranian military commander Qassem Soleimani.

The New York Times cited Iraq's Joint Military Command saying that the attack began at 1:20 a.m. local time, the time that Suleimani was killed on Friday.