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US forces early on Wednesday struck three sites used by Iran-backed militias in Iraq, Defence Secretary Lloyd Austin announced.
Mr Austin said President Joe Biden had directed US military forces to conduct “necessary and proportionate” strikes on sites used by the Iranian-backed Kataib Hezbollah militia group and other Iran-affiliated groups in Iraq.
“These precision strikes are in direct response to a series of escalatory attacks against US and coalition personnel in Iraq and Syria by Iranian-sponsored militias,” Mr Austin said in a statement.
The US military's Central Command said the strikes occurred at 12:15am on Wednesday.
They hit Kataib Hezbollah headquarters, storage and training sites for rockets, missiles and one-way attack drones, Centcom said on X.
Two militia sources in Iraq told The National that at least five strikes hit targets in the town of Jurf Al Sakhar, south of Baghdad.
There was no immediate word of any casualties and the Pentagon did not immediately disclose what weapons were used.
More strikes hit the border town of Al Qaim in western Iraq, killing two fighters and wounding two others, the militia sources said.
A video published by the militias on their social media accounts showed the aftermath of the strikes in Al Qaim.
In the video, fighters in uniform are seen digging up in the debris of a demolished building.
The strikes came after an attack on Tuesday against US forces at Ain Al Asad airbase in western Iraq.
A US defence official confirmed that attack occurred, but did not provide more detail. Another attack at the same base on Saturday injured four US personnel.
The latest US strikes in Iraq are likely to provoke an angry reaction in the country, which regards such actions as undermining its sovereignty.
On January 4, the US killed a militia commander in eastern Baghdad after he had conducted attacks on American forces in Iraq and Syria, leading to renewed calls for Iraq to request US forces to leave Iraq.
In recent months, tension has soared between US troops and Iran-backed militias in Iraq and Syria after scores of attacks against Americans forces in the two countries.
The attacks began after the outbreak of the Gaza war, which shattered the year-long calm between the militias and US forces since the establishment of Prime Minister Mohammed Shia Al Sudani’s government.
The militias say their attacks against US troops in Iraq and Syria are in response to Washington's support for Israel in its fight against Hamas.
