One official said the strikes targeted five different sites, primarily focused on weapons storage facilities. Three officials, speaking on condition of anonymity, did not name the specific militia groups being targeted.
The Pentagon earlier on Thursday squarely blamed Iran-backed militia for Wednesday's attack, which also wounded 14 people. One of the officials said the U.S. response would be proportional to that Wednesday rocket attack.
The Pentagon did not immediately respond to a request for comment.
President Donald Trump had authorized the U.S. military to respond to the attack in Iraq, in which militants fired 18 107 mm Katyusha rockets from a truck, striking Iraq's Taji military camp north of Baghdad.
Speaking from the Pentagon earlier on Thursday, Defense Secretary Mark Esper and Army General Mark Milley, chairman of the Joint Chiefs of Staff, said they believed Iran backed the fighters who carried out the attack, and warned that all options were on the table for responding.
"We gotta hold the perpetrators accountable. You don't get to shoot at our bases and kill and wound Americans and get away with it," Esper said.
U.S. Marine General Kenneth McKenzie, head of the military's Central Command, told a Senate hearing on Thursday that only the Iran-backed Kataib Hezbollah militia had been known to wage such an attack in the past.
"While we are still investigating the attack, I will note that the Iranian proxy group Kataib Hezbollah is the only group known to have previously conducted an indirect fire attack of this scale against U.S. and coalition forces in Iraq," McKenzie said.
Washington blamed Kataib Hezbollah for a strike in Iraq in December that killed a U.S. contractor, leading to a cycle of tit-for-tat confrontations that culminated in January's U.S. killing of top Iranian General Qassem Soleimani and a retaliatory Iranian missile attack that left more than 100 U.S. troops with brain injuries.
Wednesday would have been Soleimani's 63rd birthday.
In the latest attack, 14 U.S.-led coalition personnel were wounded, including American, British, Polish and others. Private industry contractors were among the wounded. Milley said five of the wounded were categorized as "urgent," suggesting serious injuries that could require rapid medical evacuation.
Britain named its fallen service member as Lance Corporal Brodie Gillon, a 26-year-old with the Irish Guards Battle Group.
The United States has not yet identified the U.S. service members killed.