Iraqi army troops have stormed into a Christian region that has been under Islamic State control since 2014, as part of US-backed operations to clear the entrances to Mosul.
The city is the militants' last major stronghold in Iraq.
A military statement said Iraqi units entered the centre of Qaraqosh, a mainly Christian town about 20km southeast of Mosul, and were carrying out mop-up operations across the town.
Further action was under way to seize a neighbouring Christian village, Karamless. The region's population fled in the summer of 2014, when Islamic State swept in.
Earlier this week, Iraqi special units also captured Bartella, a Christian village north of Qaraqosh.
A US military official estimated there were fewer than a couple of hundred Islamic State fighters in Qaraqosh.
Some 1.5 million residents remain in Mosul and worst-case scenario forecasts see up to a million being uprooted, according to the United Nations.
The army is trying to advance from the south and the east while Kurdish Peshmerga fighters are holding fronts in the east and north.
On the southern front, nearly 1000 people were treated for breathing problems linked to toxic fumes from a sulphur plant that Islamic State militants are suspected to have set on fire on Thursday, sources at the hospital of Qayyara said.
The Iraqi army's media office said about 50 villages had been taken from the militants since Monday in operations to prepare the main thrust into Mosul itself, where 5000 to 6000 IS fighters are dug in, according to Iraqi estimates.
Islamic State is relying mainly on suicide car bombs, roadside bombs, mines, sniper and mortar fire to counter the charge of the Iraqi units trained by the US to deal specifically with this kind of warfare.
The Iraqi army advance took place as US Defence Secretary Ash Carter met Prime Minister Haider al-Abadi in Baghdad to evaluate the campaign that began on Monday with air and ground support from the US-led coalition.
"The campaign is proceeding according to plan and the schedule that we've had," Mr Carter said. The Iraqi prime minister, however, rejected any Turkish participation in the campaign.
Mr Carter signalled during a visit to Ankara on Friday his support for a possible Turkish role and said there was an agreement in principle between Baghdad and Ankara - potentially ending a source of tension.
"I know that the Turks want to participate, we tell them thank you, this is something the Iraqis will handle," Mr Abadi said.
The militants retaliated to the advance of the Iraqi forces and the Kurdish fighters in Mosul on Friday by attacking Kirkuk, an oil city that lies east Hawija, a pocket they continue to control between Baghdad and Mosul.
Authorities in Kirkuk regained control of the city on Saturday.
At least 50 people have been killed and 80 others wounded in clashes between security forces and the militants in Kirkuk, according to a hospital sources.