Security sources said IS insurgents had infiltrated Imam Gharbi, some 70 km (44 miles) south of Mosul on the western bank of the Tigris river, on Wednesday evening from a pocket of territory still under their control on the eastern bank.
Reports in Iraq indicate that government forces will announce victory in Mosul in the coming hours.
"It's a matter of hours", the Iraqi state television anchor said. Isis fighters are putting up a fierce resistances with suicide bombers, snipers and grenades, hampering the progress of Iraqi troops.
In June 2017, the mosque, one of Islam's most venerated sites, along with al-Hadba minaret, was destroyed by explosions as Iraqi forces battled the ISIS terrorists who had holed up nearby.
In early June the United Nations reported that 231 civilians attempting to flee the city were shot and killed over a two week period.
Members of the Emergency Response Division celebrate in the Old City of Mosul on Saturday
A military spokesman cited by the TV said the insurgents' defence lines were collapsing. Photo Credit: Felipe Dana/AP Iraqi forces moved to besiege the Old City before launching their attack in order to prevent ISIS fighters from fleeing to neighboring Syria, but al-Aridi said hundreds of militants still managed to escape from the Old City alone.
The battle for Mosul has already displaced 90,000 people, about half the city's pre-war population, according to aid organizations.
This came as a number of the city's streets and alleys, then, had still been under the ISIS' control which were fully liberated later during operations by the Iraqi forces on July 6 and 7. Earlier, a top United Nations official for Iraq's affairs said more than $1 billion would be needed to reconstruct the city following its liberation.
Iraqi forces backed by a USA -led coalition launched a major operation to retake the city in October 2016.