The US military on Thursday (February 25) struck Iran-backed militias in eastern Syria, killing at least 22 fighters, in what the Pentagon said was a message from the new administration after recent rocket attacks targeting US troops in Iraq.
In its first military action against Iran-linked groups since Joe Biden became president, the Pentagon said it had carried out airstrikes at a Syria-Iraq border control point used by Iran-backed groups, destroying "multiple facilities".
The US raids, carried out Thursday night "at President Biden's direction" targeted "infrastructure utilised by Iranian-backed militant groups in eastern Syria", Pentagon spokesman John Kirby said in a statement.
"These strikes were authorised in response to recent attacks against American and coalition personnel in Iraq, and to ongoing threats to those personnel," he said.
"Specifically, the strikes destroyed multiple facilities located at a border control point used by a number of Iranian-backed militant groups, including Kataib Hizbullah and Kataib Sayyed al-Shuhada," he said.
"This proportionate military response was conducted together with diplomatic measures, including consultation with coalition partners," Kirby said.
"The operation sends an unambiguous message: President Biden will act to protect American and coalition personnel," he added. "At the same time, we have acted in a deliberate manner that aims to de-escalate the overall situation in both eastern Syria and Iraq."
The Syrian Observatory for Human Rights said at least 22 fighters were killed when the strikes occurred near the Syrian border town of Albu Kamal.
Militia border posts also were destroyed, the Observatory said.
It said all the dead were from Iraqi Kataib Hizboullah and similar groups.
Kirby said the location was used by Kataib Hizbullah and Kataib Sayyed al-Shuhada, two Iran-aligned Iraqi militias.
Reprisal for rocket attacks
The US action followed three rocket attacks on facilities in Iraq used by US and coalition forces fighting the "Islamic State of Iraq and Syria" (ISIS).
A February 15 strike on a military complex at Erbil airport in northern Iraq's Kurdish region killed a civilian and a foreign contractor working with coalition forces, and wounded several US contractors and a soldier.
The attacks in Iraq laid down a challenge to the new Biden administration just as it opened a door to resumed negotiations with Tehran over its nuclear programme.
Last week, the administration offered talks with Iran led by European allies as it mulls a possible return to a 2015 nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA).
But the administration has also made clear it will not brook "malign activities" in the region by Iran.
A shadowy group calling itself Awliyaa al-Dam (Guardians of Blood) claimed responsibility for the Erbil attack, but US and Iraqi security officials said they believe it serves as a front group for prominent pro-Iran militias.
US Defence Secretary Lloyd Austin pointed the finger at Kataib Hizbullah.
"We're confident in the target we went after. We know what we hit," he said of the Thursday strikes, noting that the target in Syria was used by the same militia that "conducted the strikes" against US interests in Iraq.
State Department spokesman Ned Price said Monday the US would "hold Iran responsible for the actions of its proxies that attack Americans" but would not "lash out" and risk destabilising Iraq.
Gen. Kenneth McKenzie, who heads US Central Command (CENTCOM), on Wednesday issued a similar warning to Iran over attacks on Erbil and Saudi Arabia during a virtual forum hosted by the Beirut Institute, Al-Monitor reported.
McKenzie said he considers it "very dangerous" for Iranian officials to assume that an uptick in such attacks in recent weeks "can be non-attributable in some way back to Iranian policy".
"We believe that all of this ultimately emanates from Iran," McKenzie said.
Weapons smuggling route
According to Observatory sources, Iranian forces and their proxies evacuated several posts and headquarters in Albu Kamal immediately after the attack, redeploying to other positions for fear of being subjected to successive attacks.
On Monday, "reliable sources" told the Observatory the Fatemiyoun Division -- a militia comprised of Afghan fighters formed by the late IRGC Quds Force commander Qassem Soleimani -- had brought in a new weapons shipment to its positions in the west Euphrates region.
The new shipment, which included shells, missiles and ammunition, entered Syria aboard vegetable trucks from Iraq, via an unofficial crossing, sources said.
The trucks headed to al-Mazare area on the outskirts of al-Mayadeen in eastern Deir Ezzor, where Iran-backed militias are concentrated, and stored the shipment in tunnels ISIS had carved out while it was in control of the area.
Similar shipments have been reported in recent weeks, the Observatory said.