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Iraqi forces enter ISIS-held town of Hit, thousands escape fighting

  • Smoke rises as people flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)

    Smoke rises as people flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)  (The Associated Press)

  • Iraqi security forces check identification documents at a checkpoint near the entrance to Ramadi, 70 miles (115 kilometers) west of Baghdad, Iraq, Sunday, April 3, 2016. Thousands of civilians have returned to the city after Iraqi government forces retook the Anbar provincial capital from the Islamic State group earlier this year. (AP Photo/Khalid Mohammed)

    Iraqi security forces check identification documents at a checkpoint near the entrance to Ramadi, 70 miles (115 kilometers) west of Baghdad, Iraq, Sunday, April 3, 2016. Thousands of civilians have returned to the city after Iraqi government forces retook the Anbar provincial capital from the Islamic State group earlier this year. (AP Photo/Khalid Mohammed)  (The Associated Press)

  • People flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)

    People flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)  (The Associated Press)

  • Smoke rises as people flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)

    Smoke rises as people flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)  (The Associated Press)

  • Iraqi security forces check identification documents at a checkpoint near the entrance to Ramadi, 70 miles (115 kilometers) west of Baghdad, Iraq, Sunday, April 3, 2016. Thousands of civilians have returned to the city after Iraqi government forces retook the Anbar provincial capital from the Islamic State group earlier this year. (AP Photo/Khalid Mohammed)

    Iraqi security forces check identification documents at a checkpoint near the entrance to Ramadi, 70 miles (115 kilometers) west of Baghdad, Iraq, Sunday, April 3, 2016. Thousands of civilians have returned to the city after Iraqi government forces retook the Anbar provincial capital from the Islamic State group earlier this year. (AP Photo/Khalid Mohammed)  (The Associated Press)

  • People flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)

    People flee their homes during clashes between Iraqi security forces and Islamic State group in Hit, 85 miles (140 kilometers) west of Baghdad, Iraq, Monday, April 4, 2016. Families, many with small children and elderly relatives say they walked for hours Monday through desert littered with roadside bombs to escape airstrikes and clashes. (AP Photo/Khalid Mohammed)  (The Associated Press)

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.