Iraqi forces have taken a strategically important town close to western Mosul on the third day of their renewed push against so-called Islamic State (IS).
The taking of Abu Saif means troops now have a direct line of sight to the Mosul's airport and its heavily-populated western areas.
But a network of tunnels under the small town means there is still resistance, reports the BBC's Quentin Sommerville from the scene.
Eastern Mosul was liberated last month.
Our correspondent, who is embedded with Iraqi forces, says troops are now trying to secure Abu Saif.
Police special forces are moving through the streets and across rooftops, backed by helicopters and artillery.
An airstrike overnight destroyed a house full of suspected IS fighters, killing all seven people inside.
Troops had come under heavy fire as they advanced on the town. Progress had been slowed by improvised bombs planted by IS along the route.
The bodies of some IS fighters were seen by the roadside, apparently hit by mortar fire or other artillery.
As the army reached Abu Saif, a small group of civilians waving a white flag was spotted.
Thousands of Iraqi troops, backed by artillery and air power, are involved in the assault to retake Mosul - and have now all but surrounded western parts of the city.
The UN has voiced concern about the welfare of civilians trapped in the city, amid reports that they could number up to 650,000.
Leaflets warning residents of an imminent offensive were earlier dropped over western Mosul.
Military officials say western districts, with their narrow, winding streets, may prove a bigger challenge than the east.
Although slightly smaller than the east, western Mosul is more densely populated and includes districts seen as pro-IS.
All bridges linking the east and west of the city, across the Tigris river, were destroyed in the earlier offensive.
That began on 17 October, more than two years after jihadists overran Mosul as they spread across much of northern and western Iraq.
The UN said in late January that almost half of all the casualties in Mosul were civilians.
At least 1,096 have been killed and 694 injured across Nineveh province since the start of October.