u.s. air- strikes are supporting the assault. prime minister haider al-abadi tweeted the first stage was "swift and decisive." it began by capturing several villages near makhmur, about 40 miles south of mosul. the ultimate goal is to reclaim mosul itself. isis forces captured the city in june of 2014, routing government troops, who left behind troves of weapons and ammunition, even american-supplied vehicles and artillery pieces since then, iraq's army, supported on the ground by shiite militias and iranian advisors, has retaken tikrit, oil-rich beiji and most recently ramadi. but mosul, which once had a population of two million, is by far its biggest challenge. in washington today, state department spokesman mark toner said the u.s. is standing by its ally. >> we certainly support and share with the iraqi government its goal of liberating mosul as quickly as possible, but this has to be an iraqi led effort. >> reporter: already, there's been an american casualty linked to the battle for mosul. a u.s. marine was killed saturday by a rocket attack near there. his newly deployed unit