US President Donald Trump has authorised the American military to respond to the March 11 rocket attack in Iraq that killed two US troops and one British service member. The order came on March 12 after the Pentagon said it had concluded that the attack was carried out by Iran-backed militia.

US Defence Secretary Mark Esper and Army General Mark Milley, chairman of the Joint Chiefs of Staff, did not name any specific militia as suspected of firing the 30 rockets said to have been used in the assault, although reports out of Washington have cited officials pointing the finger at Iran-backed Kataib Hezbollah. They made it clear, however, that they contend that Iran backed the fighters who carried out the attack, and, Reuters reported, they warned that all options were on the table.

“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.

“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 that it was not “fully determined it was Iran” and did not disclose what the US might do in retaliation. “We’ll see what the response is,” he said.

“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 added.

Washington blamed Kataib Hezbollah for a strike in December that killed a US contractor. A sequence of tit-for-tat confrontations that followed led to Trump in early January ordering the assassination of second post powerful Iranian official, Major General Qasem Soleimani. A retaliatory Iranian missile attack came in response, causing no fatalities but leaving more than 100 US troops with brain injuries.

In the latest attack, which came on what would have been Soleimani’s 63rd birthday, 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”.

The US-led military coalition in Iraq said that 107 mm Katyusha rockets struck Iraq’s Taji military camp in the attack. A US official briefed Reuters that 30 rockets were fired from a nearby truck but that only 18 of them landed at the Iraqi base.

Iran-backed paramilitary groups have regularly been rocketing and shelling bases in Iraq that host US forces and the area around the US Embassy in Baghdad, US officials say.