A spokesman for the paramilitary groups said the advance towards the Islamic State-held town of Tal Afar, about 55 km (35 miles) west of Mosul, would start within 'a few days or hours'. Photograph: (AFP)
The move could block any retreat by the IS into Syria, but western countries fear the fighters could alienate residents in mainly Sunni area
Iraqi Shi'ite militias backed by Iran said on Friday they would soon join the fight against Islamic State on a new front west of Mosul, a move which could block any retreat by the jihadists into Syria but might alarm Turkey and the United States.
The Shi'ite militias, with thousands of battle-hardened fighters trained by Iran, would bring important extra firepower to what is expected to be the biggest battle in Iraq since the US-led invasion in 2003.
But their arrival on the battlefield in one of the most diverse parts of Iraq also creates worry for Western countries backing the Iraqi government offensive, who fear that the Shi'ite fighters could alienate residents in mainly Sunni areas.
A spokesman for the paramilitary groups said the advance towards the Islamic State-held town of Tal Afar, about 55 km (35 miles) west of Mosul, would start within "a few days or hours".
If successful, the offensive would leave Islamic State fighters - and the 1.5 million civilians still living in Mosul - encircled by an advancing coalition of forces which seeks to crush the hardline Sunni militants in their Iraq stronghold.
As many as 50,000 Iraqi soldiers, police and Kurdish peshmerga fighters, backed by US-led air strikes and support on the ground, have advanced on Mosul for nearly two weeks from the south, north and east.
They have already recaptured scores of villages on the flat plains east of Mosul and along the Tigris river to the south of the city, Islamic State's last big bastion in Iraq.
Until now, it has not been clear whether the Shi'ite paramilitaries would join the fight, or whether the western approaches of the city would be left open so that civilians and militants could escape.
Rights groups have called on Baghdad to keep the Shi'ite militias away from the battlefield, accusing them of carrying out revenge killings and kidnappings in other areas freed from Islamic State. The militias and the Baghdad government say any such abuses were isolated incidents and not widespread.
The battle for Mosul itself, a city many times larger than any other ever held by Islamic State, is expected to be the biggest military operation in Iraq since US troops invaded to topple former president Saddam Hussein nearly 14 years ago.
Adding to the challenges facing the advancing forces, retreating Islamic State fighters have forced women and children from outlying villages to march alongside them as human shields as they withdraw into the city, according to villagers who spoke to Reuters by telephone from Mosul.
Older boys and men of fighting age were taken off to an unknown fate, they said.
The United Nations said on Friday Islamic State had abducted 8,000 families from around Mosul to use as human shields, and had killed 232 people near the city on Wednesday who refused to comply with orders.
The group's "depraved, cowardly strategy is to attempt to use the presence of civilians to render certain points, areas or military forces immune from military operations, effectively using tens of thousands of women, men and children as human shields," UN high commissioner for Human Rights Zeid Ra'ad al Hussein said.
A man who was among those taken to Mosul from a village south of the city described the exodus for those forced to retreat with the fighters as human shields.
"They put us in a trailer pulled by a tractor, and along the way we saw civilians shot dead with bullets in the head on both sides of the road; about ten, all of them men," said the man, speaking from one of the few parts of Mosul where mobile phone coverage still works. "We are in shock."