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 (Centcom) said in a statement the casualties were caused by a drone attack at a base in northeast Jordan, near the Syria border.
US President Joe Biden said that the attack was carried out by "radical Iran-backed militant groups".
This is the first time US soldiers have been killed in the region after Hamas's 7 October attack on Israel.
There have been attacks on US bases in the region but so far there have been no casualties reported by the US army.
The White House said Mr 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," Mr Biden said in a statement.
"Have no doubt - we will hold all those responsible to account at a time and in a manner our choosing.
"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.
Mr Biden was briefed on Sunday morning about the attack, the White House said.
The names of the servicemen killed and injured have not yet been released as officials work to notify their families.
Jordan, a close American ally, has housed US military bases for some time. It is estimated that around 3,000 American troops are typically stationed there.
Earlier this month, two Navy Seals were presumed dead by the US Army after they went missing during an operation off the coast of Somalia a to seize Iranian-made weapons bound for Houthis in Yemen.
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