The US has carried out air strikes against two weapons and ammunition storage facilities in eastern Syria used by Iran's Revolutionary Guards.
Secretary of Defense Lloyd Austin said the strikes were in response to recent attacks on US bases in Iraq and Syria by Iranian-backed militia groups.
The US strikes were "separate and distinct from the ongoing conflict between Israel and Hamas," he said in a statement.
Iran did not immediately comment.
The strikes, carried out by a pair of F-16 US air force fighters, took place on Friday at around 04:30 local time (01:30 GMT) near Abu Kamal, a town on the border with Iraq.
It is not yet known if there were any casualties from the attacks.
"These precision self-defence strikes are a response to a series of ongoing and mostly unsuccessful attacks against US personnel in Iraq and Syria by Iranian-backed militia groups that began on October 17," Mr Austin said in a statement.
