Three US troops have been killed and 25 injured in a drone attack on a US base in Jordan, the US military said.
US Central Command said in a statement the casualties were caused by a drone attack at a base near the Syria border.
US President Joe Biden said that the attack was carried out by "radical Iran-backed militant groups."
The White House said Biden was briefed Sunday morning on the attack by US Defense Secretary Lloyd Austin and other officials.
"While we are still gathering the facts of this attack, we know it was carried out by radical Iran-backed militant groups operating in Syria and Iraq," Biden said in a statement.
"Jill and I join the families and friends of our fallen - and Americans across the country - in grieving the loss of these warriors in this despicable and wholly unjust attack," the statement added.
The names of the servicemen killed and injured have not yet been released as officials work to notify their families.
In December, US officials said that US bases in Iraq and Syria have been attacked at least 97 times since 17 October.
Last month, the US carried out airstrikes against Iran-affiliated groups after three US servicemembers were injured, one critically, in a drone attack on a base in northern Iraq.
Earlier in January, one retaliatory US strike in Baghdad killed a militia leader accused of being behind attacks on US personnel.
It is not clear who is behind this latest attack, though President Biden vowed to "hold all those responsible to account at a time and in a manner our choosing."
In a pre-recorded interview with ABC News that aired on Sunday morning, Chairman of the Joint Chiefs of Staff Gen CQ Brown said that America's aim in the region is to "not have the conflict broaden."
"The goal is to deter them and we don't want to go down a path of greater escalation that drives to a much broader conflict within the region."
US and coalition troops are also stationed in the Red Sea after the Iran-backed Houthis began attacking commercial ships in the region. The Yemen-based group says it is targeting vessels in the region in support of Palestinians in Gaza, where Israel is fighting Hamas.
The US Central Command (Centcom) has previously said "these unlawful actions have nothing to do with the conflict in Gaza".
"The Houthis have fired indiscriminately into the Red Sea, targeting vessels impacting over 40 countries around the world," Centcom has said.
Two Navy Seals are presumed dead by the US Army after they went missing in January during an operation off the coast of Somalia a to seize Iranian-made weapons bound for Houthis in Yemen.-BBC
