Iraqi forces take a position on the roof of a building as they advance towards Mosul's Old City on June 18, 2017.
The mosque, with its famous leaning minaret, has become symbolic in the Iraqi military’s fight against the militant group, after ISIS leader Abu Bakr al-Baghdadi proclaimed a caliphate from the mosque in July 2014.
Above: Smoke billows from Mosul's Old City.
Iraqi forces stand amidst the rubble of a building as they advance towards Mosul's Old City.The ground forces are being supported by the U.S.-led coalition as well as Iraqi war planes.
Iraqi soldiers look out from a tank as they advance towards the Islamic State militants positions in the Old City in western Mosul.
Around 100,000 civilians remain trapped in the city, according to the United Nations.
Above: Residents walk through a damaged street as troops advance.
Iraqi forces advance towards Mosul's Old City.
A bullet-riddled vehicle belonging to the Iraqi forces.
Iraqi forces hold a position inside a damaged building. The offensive follows months of fighting as Iraqi forces attempt to liberate the country’s second-largest city.
A member of the Iraqi forces leaves a damaged building carrying a kettle at an army position as troops advance towards Mosul's Old City.
Iraqi soldiers eat their meal along the road beside their armored fighting vehicles in western Mosul.
The wider campaign to drive out ISIS from Mosul began in November last year.
Above: Iraqi forces advance towards Mosul's Old City.
Lt. Col. Abdulrahman Al-Khazali told NBC News that the police had advanced through the Old City from the south in order to recapture the mosque.
Above: Iraqi forces climb over rubble as they advance towards Mosul's Old City.
A member of the Iraqi forces rests inside a house.
A displaced Iraqi civilian walks along a road littered with debris and destroyed vehicles.