Iraqi forces have pushed into a town south of Mosul after Islamic State fighters fled with civilians used as human shields, officials said.
State-sanctioned Shiite militias joined the offensive by opening up a new front to the west.
Iraqi troops approaching Mosul from the south advanced into Shura after a wave of US-led air strikes and artillery shelling against militant positions inside the town.
Commanders said most of the IS fighters withdrew earlier this week with civilians, but that US air strikes had disrupted the forced march, allowing some civilians to escape.
"After all this shelling, I don't think we will face much resistance," Iraqi army Major General Najim al-Jabouri said.
"This is easy, because there are no civilians left," he added. "The big challenge for us is always the civilians."
Lieutenant Colonel Hussein Nazim, of the militarised Federal Police, which is leading the advance from the south, said some civilians, mainly the elderly and infirm, might still be in the city, but that the use of heavy artillery and air strikes was a standard tactic.
"We must strike like this before we move in or else we will be easy prey for Daesh," he said, using an Arabic acronym for IS.
Iraqi forces launched a massive operation to retake militant-held Mosul last week.
The offensive to retake Iraq's second largest city, which is still home to more than one million people, is expected to take weeks, if not months.
State-sanctioned Shiite militias, meanwhile, launched an assault to the west of Mosul aimed at driving IS from the town of Tel Afar, which had a majority Shiite population before it fell to the militants in the summer of 2014.
They will also try to secure the western border with Syria, where IS shuttles fighters, weapons and supplies between Mosul and the Syrian city of Raqqa, the de facto capital of its self-styled caliphate.
The involvement of the Iranian-backed Shiite militias has raised concern that the battle for Mosul, a Sunni-majority city, could aggravate sectarian tensions.
The militias say they will not enter the city itself.
Jaafar al-Husseini, a spokesman for the Hezbollah Brigades, said his group and the other militias were advancing with the aid of Iranian advisers and Iraqi aircraft.
He said the US-led coalition, which is providing air strikes and ground support to the Iraqi military and Kurdish forces known as the peshmerga, is not playing any role in the Shiite militias' advance.
In Baghdad, meanwhile, a suicide bomber targeting an aid station for Shiite pilgrims killed at least seven people and wounded more than 20, police and hospital officials said.
No one immediately claimed the attack, but IS often targets Iraq's Shiite majority, which the Sunni extremists view as apostates deserving of death.
The Mosul offensive involves more than 25,000 soldiers, Federal Police, Kurdish fighters, Sunni tribesmen and the Shiite militias, which operate under an umbrella organisation known as the Popular Mobilisation Units.
Many of the militias were originally formed after the 2003 US-led invasion to battle American forces and Sunni insurgents.
They were mobilised again and endorsed by the state when IS swept through northern and central Iraq in 2014, capturing Mosul and other towns and cities.
Iraqi forces moving towards Mosul from several directions have made uneven progress since the offensive began on October 17.
They are six kilometres (four miles) from the edge of Mosul on the eastern front, where Iraq's special forces are leading the charge.
But progress has been slower in the south, with Iraqi forces still 35 kilometres (20 miles) from the city.
The UN human rights office said on Friday that IS has rounded up tens of thousands of civilians in and around Mosul to use as human shields, and has massacred more than 200 Iraqis in recent days, mainly former members of the security forces.
The militants have carried out mass killings of perceived opponents in the past and boasted about them in grisly photos and videos circulated online.
The extremist group is now believed to be cracking down on anyone who could rise up against it, focusing on men with military training or past links to the security forces.
There have been no major advances over the past two days, as Iraqi forces have sought to consolidate their gains by clearing explosive booby traps left by the extremists and uncovering tunnels they dug to elude air strikes.
