Iraqi forces captured the eastern side of Mosul in January after 100 days of fighting.

US-backed Iraqi army units on Wednesday took control of the last major road out of western Mosul that had been in ISIS’s hands, a general and residents there said, trapping the militants in a dwindling area within the city.

The army’s 9th Armored Division was within a kilometer of Mosul’s “Syria Gate,” the northwestern 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.

The road links Mosul to Tal Afar, another ISIS 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 Feb. 19.

If they defeat ISIS 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, ISIS’s Syria stronghold in neighboring Syria, within six months.