ABU GHADDUR, Iraq — U.S.-backed Iraqi forces on Sunday launched a multi-pronged assault to retake the town of Tal Afar, west of Mosul, marking the next phase in the country’s war on the Islamic State group.

Tal Afar and the surrounding area is one of the last pockets of IS-held territory in Iraq after victory was declared in July in Mosul, the country’s second-largest city. The town, about 93 miles east of the Syrian border, sits along a major road that was once a key IS supply route.

“The city of Tal Afar will be liberated and will join all the liberated cities,” Prime Minister Haider al-Abadi said in a televised speech early Sunday. He called on the militants to “surrender or die.”

By early afternoon, Lt. Gen. Abdul-Amir Rasheed Yar Allah, who commands the operation, said the forces had recaptured a series of villages east, southwest and northwest of town.

The U.S.-led coalition providing air and other support to the troops.

On the front lines, pillars of smoke could be seen rising in the distance as U.S. and Belgian special forces worked with Iraqi troops to establish a position on the roof of a house. They later fired mortar rounds and launched drones.

Lt. Gen. Riyad Jalal Tawfiq, of the Iraqi army, said IS had deployed small teams of attackers as well as suicide car bombs and roadside bombs.

The coalition estimates that approximately 10,000 to 50,000 civilians remain in and around Tal Afar. In past battles, IS has prevented civilians from fleeing and used them as human shields, slowing Iraqi advances.

Hours after announcing the operation, the United Nations expressed concerns over the safety of the civilians.