"The soldiers of the Counterterrorism Force are advancing very fast. I wouldn't say a matter of days but matter of hours before advancing and (to) start cleansing the city of Mosul from terrorism," General Talib Shegati said in an interview with state-run Iraqiya TV.
A coalition of around 100,000 Iraqi-led forces have been in a decisive push toward Mosul since October 17 to end more than two years of the militant group's brutal rule.
On Monday, forces began advancing on the city from three separate fronts at dawn.
Experts have said that entering Mosul will likely trigger the fiercest fighting seen yet in the offensive, and that the battle is expected to be fought "street to street."
Mosul has been an ISIS stronghold for more than two years, and although the ISIS fighters are vastly outnumbered, they have put up fierce resistance in pockets of the territory around the city. US defense officials have said there are up to 5,000 ISIS militants fighting back in this offensive.
Since the offensive began, they have carried out mass executions of civilians
, lit toxic sulfur and oil fires to fend of coalition forces, and used civilians as human shields to ward off air strikes.
They are carrying out regular suicide vehicle bombings and witnesses have told CNN that they are rigging bridges and laying booby traps inside the city.
On the eastern edge of the city in the town of Gogjali, witnesses told CNN that they could see Iraqi forces in open land nearby, and that families had begun fleeing their homes after hearing gunfire and explosions, as well as several airstrikes.
The witnesses said that there were around 40 ISIS militants in the area who had set up mortar positions. ISIS has completely blocked the main road entering Mosul from Irbil with concrete T-walls, they said.
Tensions inside Mosul appear to be flaring as troops get ever closer. Five ISIS officials, including the head of the city's prisons, were shot dead by gunmen in a drive-by shooting near a market on Monday.
Witnesses in the city also reported further acts of resistance against the terror group Monday, telling CNN that unknown gunmen shot and killed four ISIS militants near their base at the al-Shaarein outdoor market in western Mosul.
The battle for Mosul is seen as one of the most significant in the fight against ISIS. The city is the group's Iraqi stronghold and is considered the jewel off the group's envisaged caliphate, or its so-called Islamic State.
The city is also near critical oil fields that ISIS has used to fatten its coffers, selling the resource illegally across borders.
When ISIS took Mosul in June 2014, it also took control of more than 2.5 million people, whom the group subjected to horrors.
There has been a mass exodus in the past two years, and today around 1 million people remain.