The US military has carried out strikes against two facilities in eastern Syria used by Iran's Islamic Revolutionary Guard Corps and groups it backs, the Pentagon said, in response to a spate of attacks against US forces in both Iraq and Syria.
"These precision self-defense 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," US Defense Secretary Lloyd Austin said in a statement late on Thursday.
The strikes were ordered by President Joe Biden. There was no immediate reaction from Tehran or Damascus.
"These Iranian-backed attacks against US forces are unacceptable and must stop," Austin said in the statement.
"If attacks by Iran's proxies against US forces continue, we will not hesitate to take further necessary measures to protect our people."
As tensions soar over the Israel-Palestine, US and coalition troops have been attacked at least 12 times in Iraq and four times in Syria. A total of 21 US forces have suffered minor injuries, the vast majority of them traumatic brain injuries.
Biden's message to Khamenei
President Biden has sent a rare message to Iranian Supreme Leader Ayatollah Ali Khamenei warning Tehran against targeting US personnel in the Middle East, the White House said earlier on Thursday.
"There was a direct message relayed. That's as far as I'm going to go," US National Security Council spokesman John Kirby told reporters, declining to say how it was delivered.
The United States has 900 troops in Syria, and 2,500 more in neighbouring Iraq.
There is growing concern that Israel-Palestine war could spread through the Middle East.
The United States has sent warships and fighter aircraft to the region since the Israel-Palestine war erupted on October 7, including two aircraft carriers, in what it says is an effort try to deter Iran and Iran-backed groups. The number of troops added to the region is in the thousands.
Iran warned Washington at the United Nations General Assembly over Israel's indiscriminate air strikes and artillery against Gaza.
"I say frankly to the American statesmen and military forces who are now managing the genocide in Palestine, that we do not welcome the expansion and scope of the war in the region," Foreign Minister Hossein Amir-Abdollahian said.
"But I warn if the genocide in Gaza continues, they will not be spared from this fire."