Iraqi troops on Tuesday reached the first urban areas of the Islamic State-held northern town of Tal Afar on the third day of a multi-pronged operation, said a military commander.

U.S.-trained elite forces, known as the Counter Terrorism Service, entered the al-Kifah neighborhood on the southwest edge of town, Lt. Gen. Abdul-Amir Rasheed Yar Allah, who commands the operation, said in a statement. He didn’t give more details.

Brig. Gen. Haider Fadhil, of the Iraqi special forces, told The Associated Press that the advancing troops didn’t face tough resistance from IS fighters, though they did fire rockets, sent suicide car bombers and used roadside bombs.

Gen. Fadhil expected the fighting to get even heavier as they push into the town’s center which is about 4.5 km (about 3 miles) away. Civilians were not seen fleeing the area, he added.

The U.S.-backed operation was launched on Sunday, a month after Iraq declared victory over IS in Mosul, the country’s second largest city. Tal Afar, about 150 km (93 miles) east of the Syrian border, is in one of the last pockets of IS-held territory in Iraq.

Along with the special forces, Iraq’s regular army, militarized Federal Police and Shia-dominated paramilitary forces are taking part in the assault. Iraq’s state-run TV aired live footage showing pillars of smoke rising in the distance as military vehicles traveled through wide, arid areas.

Iraqi forces have driven IS from most of the major towns and cities seized by the militants in the summer of 2014, including Mosul, which was retaken after a grueling nine-month campaign.

But along with Tal Afar, the militants are still fully in control of the northern town of Hawija as well as Qaim, Rawa and Ana, in western Iraq near the Syrian border.