about a kilometer away from palaces. isis has been putting up tough fight there militants have planted ieds on roads and a bridge that cross into that city. isis of course is a common enemy for groups that once fought each other. for example, iraq's sunni and shia militias. iran is also playing a big role in the fight against isis in iraq. and as becky anderson reports, that's a big cause for concern in the region. >> reporter: the operation to retake tikrit is the biggest undertaken by the iraqi government thus far. a fighting force in excess of 25,000 comprising iraqi troops and importantly an assortment of both sunni and shia militia, hoping to wrestle back the strategic city from isis. and playing a prominent role, this man. kasem sulimani head of iran's elite quds force.