the fighting.

More than 3,000 Iraqi troops took part in the assault under heavy U.S.-led coalition air support, but the pace of the fight also slowed as Iraqi forces moved from fighting in more rural areas with few civilians to the tight, narrow streets of Mosul proper. At least seven suicide attackers in explosives-laden vehicles attacked troops on Friday, five of whom were killed before nearing their targets.

The operation to retake Mosul is expected to take weeks if not months. Moving from neighborhood to neighborhood in house-to-house battles through dense warrens of booby-trapped buildings is time consuming and Iraq's military has repeatedly opted for slower operations in an effort to minimize casualties.

Some 1 million civilians still remain in the city, complicating the advance. IS militants have driven thousands ofresidents deeper into the city's built-up areas to be used as human shields, while hundreds of others have fled toward government-controlled territory and thousands have headed west into Syria.

Mosul is the last major IS stronghold in Iraq, and expelling the militant group from the city would be a major blow to the survival of its self-styled "caliphate" that stretches into Syria.

Iraqi forces have made uneven progress in closing in on the city since the operation began on Oct. 17. Advances have been slower from the south, with government troops still some 20 miles (35 kilometers) away. Kurdish fighters and Iraqi army units are deployed to the north, while government-sanctioned Shiite militias are sweeping in from the west to try to cut off any IS escape route.