US-backed Iraqi army units on Wednesday took control of the last major road out of western Mosul that had been in Islamic State's hands, a general and residents there said, trapping the militants in a dwindling area within the city.
The army's ninth Armoured Division was within a kilometre of Mosul's "Syria Gate", the north-western entrance of the city, a general from the unit told Reuters by telephone.
"We effectively control the road, it is in our sight," he said. Mosul residents said they had not been able to travel on the highway that begins at the "Syria Gate" since Tuesday.
To secure Mosul, Iraq army makes desert push with US help
The road links Mosul to Tal Afar, another Islamic State stronghold 60 km (40 miles) to the west, and then to the Syrian border.
Iraqi forces captured the eastern side of Mosul in January after 100 days of fighting and launched their attack on the districts that lie west of the Tigris River on February 19.
If they defeat Islamic State in Mosul that would crush the Iraq wing of the caliphate declared by the group's leader Abu Bakr al Baghdadi in 2014.
The US commander in Iraq has said he believes US-backed forces will recapture both Mosul and Raqqa, Islamic State's Syria stronghold in neighbouring Syria, within six months.
The Pentagon says around 450 US military advisers are currently assisting Iraqi partners in the fight for Mosul, performing roles including providing guidance and calling in air strikes.
But US forces have been involved in firefights with the militants, a spokesman acknowledged this month.