MOSUL, Iraq — The Iraqi advance into Mosul’s western half slowed Saturday as combat turned to urban warfare and Iraqi forces met stiff resistance from the Islamic State group. Hundreds of civilians poured out of Mosul on foot following the advances, but the vast majority of 750,000 estimated to still be in the city’s west remain trapped, and describe deteriorating humanitarian and security conditions.

Special forces Lt. Gen. Abdul-Wahab al-Saadi said that his troops are “moving very slowly” and that Islamic State fighters are responding with car bombs, snipers and dozens of armed drones.

The drones have caused relatively few deaths, but have inflicted dozens of light injuries that have disrupted the pace of ground operations.

Similar to the way operations inside eastern Mosul initially unfolded, in west Mosul, Islamic State fighters repeatedly brought Iraqi convoys to a halt Saturday with small teams of one or two men and a handful of car bombs.

Al-Saadi said the Mamun neighborhood was particularly difficult because its streets are not organized in a grid. “The roads are random,” he said.

The difficulty foreshadows obstacles Iraqi forces expect to face in the narrow alleyways of western Mosul’s historic district.