Baghdad, Arbil: An Iran-backed paramilitary force said it would support the Iraqi army’s offensive on Mosul, Daesh’s last major stronghold in Iraq, raising the risk of sectarian strife in the mainly Sunni region.

The Popular Mobilisation Force (PMF), a coalition of mostly Iranian-trained Shiite militias, said late on Tuesday it would back Iraqi government forces advancing towards Tal Afar, about 55km west of Mosul.

Taking Tal Afar would effectively cut off the escape route for militants wanting to head into neighbouring Syria and would please the Iran-backed army of Syrian President Bashar Al Assad.

It has accused the US-led anti-Daesh coalition of planning to allow the terrorists such a safe passage.

But it could also hamper the escape of civilians from the area of Mosul, which is Iraq’s second biggest city and where the militants are reportedly trying to use residents as human shields.

Iraqi Prime Minister Haider Al Abadi said on Tuesday that blocking the road to Syria was the responsibility of the coalition that is providing air and ground support to Iraqi and Kurdish troops engaged in the battle.

Tal Afar’s pre-war population of about 150,0000 to 200,000 was a mix of Sunni and Shiite ethnic Turkmens until Shiites fled the town after Daesh’s ultra-hardline Sunni militants took over the region in 2014, declaring a ‘caliphate’ over swathes of Iraq and Syria.

“The Iranians and the (PMF) plan to take Tal Afar because of the Shiite significance and use that as a way to angle in to Mosul,” said a senior Iraqi official who asked not to be named. “But they also want to use it as a way to angle into the Syria fight.”

Iraqi government forces are mostly fighting on the southern front and were trying on Wednesday to clear the region of Shora, 40km south of the city, a military statement said.

Kurdish Peshmerga fighters were deployed on the eastern and northern front-lines, 20km to 25km from the city.

“The PMF will be backing the security forces on the western front (..) along two axes. The first is Tal Afar and the second is to support the forces going into the centre of Mosul,” a statement on the PMF website said.

The announcement came despite warnings from human rights groups that PMF involvement could ignite sectarian violence.

Shiites make up a majority in Iraq but Sunnis are predominant in the north and the west of the country.

The PMF officially reports to the Shiite-led government of Al Abadi, who announced on Monday the start of the Mosul offensive.

It was formed in 2014 to help push back Daesh’s sweeping advance through the northern and western provinces.

Al Abadi has sought to allay fears of sectarian bloodshed, saying that the army and the police will be the only forces allowed to enter the city.

Amnesty International on Tuesday published a report saying the Iran-backed militias had committed “serious human rights violations, including war crimes” against civilians fleeing Daesh-held territory.

The United Nations said in July it had a list of more than 640 Sunni men and boys reportedly abducted by a Shiite militia in Fallujah, a former militant stronghold west of Baghdad, and about 50 others who were summarily executed or tortured to death.

The government and the PMF say a limited number of violations did occur and were investigated, but they deny the abuses were widespread and systematic.

Iraqi officials and residents of Mosul say Daesh is preventing people from leaving the city but civilians are fleeing from outlying districts and villages.

The United Nations has warned that some 100,000 people may arrive in Syria from the Mosul area. Save the Children said on Wednesday about 5,000 people, mostly women and children, had arrived at the Al Hol camp in Syria in the last 10 days.

“At least a thousand more are now massing at the border waiting to cross,” the organisation said in a statement.