US fighter jets struck two targets in Iraq early on Wednesday, killing eight pro-Iran fighters in retaliation for repeated attacks on American troops, US and Iraqi sources said.
The twin strikes, which followed similar bombardment of Iran-backed forces on Tuesday, drew condemnation from the Iraqi government, which said it had not been consulted about the military action on its soil.
The US military "conducted discrete, precision strikes against two facilities in Iraq," US Central Command said on X, previously Twitter.
"The strikes were in direct response to the attacks against US and coalition forces by Iran and Iran-backed groups," the post added.
The Iran-backed Hezbollah Brigades, which form part of the Hashed al-Shaabi (Popular Mobilisation) force within Iraq's armed forces, said the strikes killed eight of its fighters.
Hours earlier, a warplane struck the vehicle of Iranian-backed fighters after they had fired a short-range ballistic missile at US and allied personnel, the Pentagon said.
It was the first time the United States has announced a strike on Iran-backed forces in Iraq since they launched a flurry of attacks against US targets in response to Washington's support for Israel in its war to destroy Hamas.
Washington has targeted Iran-backed groups in neighbouring Syria, however, carrying out strikes on three occasions in recent weeks.
Since the Gaza war erupted with a deadly Hamas attack on Israel on October 7, US forces deployed in Iraq and Syria have been attacked at least 66 times, most recently on Monday night, according to Pentagon officials.
"We can confirm an attack last night by Iran-backed militias using a close-range ballistic missile against US and coalition forces at Al-Asad Airbase, which resulted in eight injuries and some minor damage to infrastructure," Pentagon spokesman Brigadier General Pat Ryder said on Tuesday.
- 'Self-defence strike' -
The Ain al-Asad Air Base lies in Anbar province, west of Baghdad, and hosts forces of the US-led coalition fighting the Islamic State (IS) group in Iraq.
"Immediately following the attack, a US military AC-130 aircraft in the area conducted a self-defence strike against an Iranian-backed militia vehicle and a number of Iranian-backed militia personnel involved in this attack. This self-defence strike resulted in several enemy KIA (killed in action)," Ryder said.
Government spokesman Bassem al-Awadi said the pre-dawn strikes on Tuesday and Wednesday were carried out "without the knowledge of Iraqi government agencies" and constituted an "unacceptable violation of Iraqi sovereignty".
But he also criticised the Iran-backed groups that have repeatedly attacked Iraqi bases used by forces of the US-led coalition fighting IS.
"Any armed action or activity outside the military institution is deemed condemnable and an unlawful endeavour that jeopardises the national interest," he said in a statement.
Pentagon Deputy Press Secretary Sabrina Singh told reporters in Washington that US forces "have been attacked approximately 66 times since October 17 -- 32 separate times in Iraq and 34 separate times in Syria."
She said the attacks had resulted in approximately 62 injuries to US personnel, but that number did not include the eight cited by Ryder.
It comes amid a relentless Israeli offensive against Hamas that the Gaza health ministry says has killed 14,100 people, thousands of them civilians.
Israel has vowed to destroy Hamas in response to its shock cross-border attack from Gaza on October 7 that Israeli officials say killed about 1,200 people, most of them civilians.
While US forces have been targeted in both Iraq and Syria, Washington had until now only responded with strikes in Syria in an apparent bid to avoid inflaming political tensions in Iraq, which the United States invaded in 2003 and where Iran wields substantial influence.
There are roughly 2,500 US troops in Iraq and some 900 in Syria as part of efforts to prevent a resurgence of IS.