Iran struck back at the United States early Wednesday for killing a top Revolutionary Guard commander, firing a series of ballistic missiles at two military bases in Iraq that house American troops in a major escalation between the two longtime foes.

It was Iran’s most direct assault on America since the 1979 seizing of the U.S. Embassy in Tehran, and Iranian state TV said it was in revenge for the U.S. killing of Revolutionary Guard Gen. Qassem Soleimani, whose death last week in an American drone strike near Baghdad prompted angry calls to avenge his slaying. A U.S. and Iraqi officials said there were no immediate reports of casualties, though buildings were still being searched. The Iraqi government later confirmed there were no casualties among Iraqi forces.