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Iraqi Shiite militias backed by Iran launched two attacks against US troops in Iraq and Syria late on Sunday.
The drone attacks came several hours after a US air strike killed five militiamen outside the northern city of Kirkuk.
The latest militia attacks hit Ain Al Asad base in western Iraq, a vast Iraqi and US military complex, and the “Green Village” area inside Syria, a much smaller base, said the Islamic Resistance in Iraq.
The Islamic Resistance in Iraq is a network of Tehran-allied militias operating in Iraq and Syria.
The group did not give details on when or how its fighters were killed but said they died in the “battle for the righteousness against falsehood of the forces of the American occupation in Iraq”.
They have vowed more “painful strikes until they [Americans] are humiliated and expelled from the sacred places”.
The influential Al Nujaba militia group acknowledged that five of its fighters had been killed in the US air strike and published their pictures on its social media accounts.
The unit is a brigade in the Popular Mobilisation Forces, an umbrella grouping of paramilitary forces consisting primarily of powerful Iran-backed militias.
A US military official confirmed the “self defence” strike carried out in northern Iraq on a drone staging site.
He said the strike took place “in the vicinity of Kirkuk” and was meant to eliminate “an imminent threat”.
The air strike came after the Islamic Resistance in Iraq claimed responsibility for a drone attack on US troops in northern Iraq and a rocket attack in Syria.
Iran's proxy groups have increased drone and rocket attacks against US forces in Iraq and Syria due to Washington's support for Israel in the Gaza war, which began after Hamas operatives killed about 1,200 people, most of them civilians, in Israel on October 7.
Apart from the Ain Al Asad attack, there were strikes on a military base near Baghdad's international airport, Harir airport in the northern city of Erbil and bases inside Syria.
The US has 900 troops in Syria and 2,500 in neighbouring Iraq to advise and assist local forces trying to prevent a resurgence of ISIS, which in 2014 seized vast areas of both countries but was later defeated.
