A US air strike has targeted facilities belonging to a powerful Iranian-backed Iraqi armed group in Syria.
A spokesman for the Kataeb Hezbollah militia, or Hezbollah Brigades, said one of its militiamen was killed and several others injured.
The official said the assault took place along the border between the Syrian site of Boukamal and Qaim, on the Iraqi side.
The Pentagon said the strikes were a retaliation for a rocket attack in Iraq earlier this month, that killed a civilian US contractor and wounded a US service member and other coalition troops.
Biden administration officials condemned the 15 February rocket attack near the city of Irbil, Iraq, but as recently as this week indicated they had not determined for certain who carried it out.
Following the strike, US Defense Secretary General Lloyd Austin said: "I'm confident in the target that we went after, we know what we hit."
Mr Austin said he had recommended the action to the president, adding the US "said a number of times that we will respond on our timeline".
The strike was the first military action undertaken by Joe Biden's administration.
Mr Biden's decision to launch an attack in Syria did not appear to signal an intention to widen US military involvement in the region, but rather to demonstrate a will to defend US troops in Iraq.
Pentagon spokesman John Kirby said the US action was a "proportionate military response" taken together with diplomatic measures, including consultation with coalition partners.
"The operation sends an unambiguous message: President Biden will act to protect American and coalition personnel," he said.
He added the airstrikes "destroyed multiple facilities at a border control point used by a number of Iranian-backed militant groups", including Kataeb Hezbollah and Kataeb Sayyid al-Shuhada.
The US has in the past targeted facilities in Syria belonging to Kataeb Hezbollah, which it has blamed for numerous attacks targeting American personnel and interests in Iraq.
Last week, NATO defence ministers decided to send about 3,500 extra alliance troops - including British personnel - to Iraq in a major boost to its counter-terrorism training mission in the country.
Cover image: File photo of the Pentagon (Picture: PA).