[Photos] The battle for Mosul

The U.S.-backed campaign to drive Islamic State (ISIS) out of Mosul, involving a 100,000-strong force of Iraqi troops, Kurdish fighters and Shia militias, began in October.

Advances have been slow as troops became bogged down in tough urban warfare after entering the city itself, and ISIS fought from densely-populated residential areas.

Driving the ultra-hardline group out of its Mosul stronghold will probably spell the end for the Iraqi side of its self-styled caliphate that stretches across areas of Iraq and Syria.