Iran denies it was involved in the drone attack which killed three US troops and injured 34 on a US base in Jordan, near the Syria border.
US President Joe Biden said the attack had been carried out by Iran-backed militant groups operating in Syria and Iraq.
"We shall respond," he said at a campaign event in South Carolina on Sunday.
It is the first time US soldiers have been killed by strikes in the region after Hamas's 7 October attack on Israel sparked the war in Gaza.
US media report the attack was on Tower 22, in north-east Jordan.
It has sparked fears of an escalation in the conflict in the region.