The operation comes weeks after Iraqi forces recaptured eastern Mosul across the Tigris River. On the first day of the new offensive, Iraqi Federal Police forces said they killed 79 ISIS militants, destroyed weapons facilities and regained control of 10 villages.
The prime minister described the operation as a "new dawn" in the liberation of Mosul, ISIS' last major stronghold in the country.
"Go forward with my blessing, heroic forces of Iraq," he said on state television.
ISIS seized Mosul, Iraq's second-largest city, in 2014. The offensive to retake the city began in October with a push by the Iraqi army, counter-terrorism forces, federal police and Kurdish Peshmerga fighters.
Iraqi forces have controlled the eastern part
of the city since January, but control of Mosul's west bank has eluded them. Over the past two years ISIS has dedicated much of its defensive preparations to the western portion of the city.
The area has been targeted by airstrikes in the past. This operation marks the first major ground offensive.
Iraqi forces will not be able to attack across the river because all five bridges connecting the eastern and western parts of the city are heavily damaged. The offensive is expected to come from the south and west.
Moreover, the older part of the city has warrens of alleys that are impassable to military vehicles. Save the Children warned that "the impact of artillery and other explosive weaponry in those narrow, densely populated streets is likely to be more deadly and indiscriminate than anything we have seen in the conflict so far."
Weapons, facilities destroyed
In addition to killing militants and retaking 10 villages, Iraqi Federal Police forces said they destroyed 13 booby trapped vehicles and dismantled 30 explosive devices.
Forces also destroyed five explosive belts and three tunnels and seized a store of projectiles.
On Friday and Saturday, American-made, Iraqi-owned F-16 warplanes carried out attacks in Wadi Akab industrial areas of western Mosul that destroyed multiple targets, Iraqi Joint Operation Command said.
The targets included six makeshift factories for booby trapping vehicles and two makeshift workshops for armoring vehicles, the statement said.
Additionally, forces destroyed a large warehouse of weapons and explosives, another building where foreign experts in booby trapping were stationed, two vehicles laden with explosives and two more loaded with heavy machine guns.
'People are in trouble'
The Iraqi air force dropped millions of leaflets
over western Mosul late Saturday, warning residents of an offensive by ground forces on the ISIS-held part of the city.
The leaflets said Iraqi forces would be "providing guidance and recommendations" for citizens ahead of the offensive. It also warned ISIS members to turn in their weapons and surrender "before they face their inevitable fate at the hands of our heroic forces."
As many as 800,000 civilians live in western Mosul
, according to the United Nations. UN humanitarian agencies will assist civilians caught in the fighting, the group said.
"The situation is distressing," said Lise Grande, the UN humanitarian coordinator for Iraq. "People, right now, are in trouble. We are hearing reports of parents struggling to feed their children and to heat their homes."