President Donald Trump has authorised the US military to respond to a rocket attack in Iraq that killed two American troops and a British service member, the Pentagon says, blaming Iran-backed militia.
Defence Secretary Mark Esper and Army General Mark Milley, chairman of the Joint Chiefs of Staff, stopped short of blaming Iran-backed Kataib Hezbollah or naming any specific militia.
But they were clear that they believe Iran backed the fighters who carried out the attack, and warned that all options were on the table - language suggesting the United States, Iran and the forces Tehran backs were again on a path toward renewed confrontation inside Iraq.
"I have spoken with the president. He's given me the authority to do what we need to do, consistent with his guidance," Esper told reporters at the Pentagon on Thursday.
Asked if a US response could include strikes inside Iran, Esper hinted that strikes against the militia itself were the priority.
"I'm not going to take any option off the table right now, but we are focused on the group - groups - that we believe perpetrated this in Iraq, as the immediate (focus)," he said.
Trump told reporters at the White House it was not "fully determined it was Iran" and declined to say what the United States might do.
"We'll see what the response is," he said.
No one has claimed responsibility for the attack and Iran has not commented.
The United States has repeatedly and publicly warned that killing Americans overseas constituted a red line that would trigger a US response.
"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.
Washington blamed Kataib Hezbollah for a strike in Iraq in December that killed a US contractor, leading to a cycle of tit-for-tat confrontations that culminated in January's US killing of top Iranian General Qassem Soleimani and a retaliatory Iranian missile attack that left more than 100 US troops with brain injuries.
In the latest attack, some 14 US-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 categorised 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 US service members killed.
The US-led military coalition in Iraq says 18 107 mm Katyusha rockets struck Iraq's Taji military camp.
A US official, speaking on condition of anonymity, said a total of 30 of the rockets were fired from a nearby truck and that only 18 of them landed at the Iraqi base.