US attack helicopters, gunships and artillery killed four Iran-linked militants over 24 hours in northwest Syria after rocket attacks wounded American troops in the area, the military said Thursday. “No group will strike at our troops with impunity,” General Michael Kurilla, head of the US Central Command (CENTCOM), warned in a statement. “We will take all necessary measures to defend our people.” The statement said US “forces struck at Iran-affiliated militants in the area with AH-64 Apache attack helicopters, AC-130 gunships, and M777 artillery, resulting in four enemy fighters killed and seven enemy rocket launchers destroyed.” A US official said on condition of anonymity that American troops had spotted enemy forces approaching with rocket launchers and fired at them before they could attack. Three US service members previously sustained minor injuries when several rockets hit both the Conoco and Green Village bases in Deir Ezzor, a strategic, oil-rich province bordering Iraq, on Wednesday evening. The facilities are run by the Kurdish-led Syrian Democratic Forces, allies of the United States and other coalition partners that are maintaining a mission against the remnants of the Islamic State jihadist group.