Iraq's federal police forces and army troops attacked the ISIS-held town of Hammam Al Alil, south of Mosul, on Saturday as Iraqi-led coalition forces seek to drive back ISIS militants from their last major Iraqi stronghold.

The Iraqi air force provided air cover for the assault Saturday morning, according to Iraq's Joint Military Command, reported CNN.

Iraqi troops are advancing from three fronts toward Hammam-al-Alil, about 30 km south of Mosul, and have reached the College of Agriculture at its edge, a statement said.

On Friday, the UN refugee agency said it had received reports ISIS has been instructing residents of Hammam Al Alil to hand over boys age 9 and older since the Iraqi-led offensive to recapture the country's second-largest city began October 17.

The boys are apparently being conscripted to fight on behalf of the terror group, Ravina Shamdasani, spokeswoman for the refugee agency, told a press briefing in Geneva, Switzerland, said the report.

The long-awaited assault on Hammam al-Alil, the last significant town before Mosul on the Tigris River, will add to the pressure on ISIS fighters.

During a stop on the front lines near Mosul, Iraqi Prime Minister Haider Al Abadi issued a warning to the terror group.

"My message to ISIS: If they want to save their lives, they should lay down their weapons now," Abadi told reporters, according to state-run Al Iraqiya TV. "We will punish the criminals among them, and we will hold them to account."

Iraqi military units were trying to reinforce their presence Saturday in eastern Mosul after fierce resistance stalled their progress a day earlier.

They said Iraqi troops had taken control of the neighborhoods of At Tahrir in the northeast and Kirkukli and Zuhra in the east. Other residents said that ISIS remained in control of the districts of Qudes and Karama, farther south.

ISIS claimed to have carried out a suicide car bombing early Saturday in the eastern neighborhood of Aden, saying it had killed 15 counterterrorism troops and destroyed six military vehicles.

Meanwhile, three roadside bombs in two separate locations killed 11 civilians and injured 18 more Saturday as they fled the town of Hawija on foot, security officials in Kirkuk told CNN.

Thousands of civilians have been forced from their homes as efforts to drive ISIS from Iraq gather pace, with many more expected to follow, stated the report.

The UN refugee agency said 3,000 people had been received on Friday alone at a new camp for displaced families in Hasansham in Irbil governorate, it added.