The United States on Thursday carried out an air strike in Syria against a structure belonging to Iranian-backed militia, two officials told the Reuters news agency.
The strike follows a series of recent rocket attacks against US targets in Iraq. It was approved by President Joe Biden, said the unnamed officials.
The Pentagon said the strikes were retaliation for a rocket attack in Iraq earlier this month that killed one civilian contractor and wounded a US service member and other coalition troops.
"This proportionate military response was conducted together with diplomatic measures, including consultation with coalition partners," the Pentagon's chief spokesperson, John Kirby, said in announcing the strikes, according to The Associated Press.
"The operation sends an unambiguous message: President Biden will act to protect American and coalition personnel. At the same time, we have acted in a deliberate manner that aims to deescalate the overall situation in eastern Syria and Iraq," added Kirby.
He said the US air strikes "destroyed multiple facilities at a border control point used by a number of Iranian- backed militant groups."
The Syrian Observatory for Human Rights said at least 17 members of the pro-Iranian militia were killed in the US air strike.
The head of the Observatory told AFP that "the attack destroyed at least three ammunition trucks and there were many dead."
Speaking to reporters after the strike, Defense Secretary Lloyd Austin said, "I'm confident in the target that we went after, we know what we hit.”
"We're confident that that target was being used by the same Shia militants that conducted the strikes," added Austin, who said he recommended the action to Biden.
"We said a number of times that we will respond on our timeline," Austin said. "We wanted to be sure of the connectivity and we wanted to be sure that we had the right targets."
Rocket attacks have regularly targeted Iraqi bases as well as the fortified Green Zone in Baghdad, where the US embassy is located, since the US elimination of top Iranian General Qassem Soleimani last January.
Former US President Donald Trump had warned the Islamic Republic against further attacks on American interests in Iraq and said, “Some friendly health advice to Iran: If one American is killed, I will hold Iran responsible. Think it over.”