Three service members were killed, including two Americans, and a dozen more were injured when a barrage of rockets was fired at a military base in Iraq on Wednesday.
US defence leaders on Thursday threatened a retaliatory strike against Iranian-backed Shia militia in Iraq, saying they know who launched the rockets in Iraq that killed and wounded US and coalition troops and the attackers will be held accountable.
Defense Secretary Mark Esper told reporters at the Pentagon that President Donald Trump on Wednesday night gave him the authority to do what he needs to do. It signalled a renewed spike in tensions with Iran and its proxy groups in Iraq.
“We're going to take this one step at a time, but we've got to hold the perpetrators accountable,” Esper said.
“You don't get to shoot at our bases and kill and wound Americans and get away with it.”
At the White House, Trump said the attackers were a rebel group that "mostly likely looked like it could be backed by Iran. And we'll see what the response is.”
Esper and Army General Mark Milley, chairman of the Joint Chiefs of Staff, declined to provide any more information about any impending US retaliation for the attack at Camp Taji north of Baghdad. But Esper said all options are on the table.
Asked if any counterattack could include a strike inside Iran, Esper said, “We are focused on the group that we believe perpetrated this in Iraq.”
Two US troops and one British service member were killed and 14 other personnel at the base were wounded when 18 rockets hit the base on Wednesday.
US officials have not publicly said what group they believe launched the rocket attack, but Kataib Hezbollah, an Iranian-backed Shia militia group, is likely behind it.
Washington blamed Kataib Hezbollah for a strike in December that killed a US contractor, leading to a cycle of tit-for-tat confrontations earlier this year that culminated in January's US killing of top Iranian general Qasem Soleimani and a retaliatory Iranian missile attack that left more than 100 US troops with brain injuries.
Tensions between Washington and Tehran have mostly played out on Iraqi soil in recent months.
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.