Iraqi forces say they have entered the town of Hit, a week after launching an operation to retake the town from Islamic State group fighters.

Commanders on the scene from Iraq's elite counterterrorism forces, who are leading the offensive, said Monday they are clearing IS fighters from Hit's northern neighborhoods as they push toward the town center.

Hit lies along an IS supply line that links the extremist militants in Iraq to those in Syria.

Thousands of civilians are fleeing as Iraqi troops advance under cover of heavy airstrikes and artillery fire. Families, many with small children and elderly relatives, say they walked for hours through desert littered with roadside bombs to escape the violence. Iraq's counterterrorism forces estimate more than 20,000 civilians are trapped inside the town.