Iraqi Shia militias massed fighters to sever remaining ISIL supply routes to Mosul, closing in on the road that links the Syrian and Iraqi parts of the group's self-declared caliphate.
Five weeks into the US-backed offensive on Mosul, the Islamic State of Iraq and the Levant group is fighting in the area of Tal Afar, 60km to the west, against the Popular Mobilisation Forces - a coalition of mostly Iranian-backed Shia armed groups sanctioned by Baghdad.
Cutting the western road to Tal Afar would seal off Mosul as the city is already surrounded to the north, south and east by Iraqi government and Kurdish Peshmerga forces.
The government's US-trained Counter Terrorism Service unit breached ISIL's defences in east Mosul at the end of October and is fighting to expand a foothold it gained there.
The road to Tal Afar is no longer safe, said a lorry driver who used it two days ago to bring in fruit and vegetables from Raqqa, ISIL's Syrian stronghold.
He said that he saw three trucks burning on the road while fighting raged in the vicinity.
"This is the last time I drive on this road, it will be cut," he told Reuters news agency by telephone, asking not to be identified as ISIL punishes by death those caught communicating with the outside world.
READ MORE: Battle for Mosul - ISIL's innocent victims
The Shia militias' involvement around Sunni-majority Mosul and their targeting of Tal Afar have proved deeply divisive.
Alleged executions and abuses carried out by fighters in territory taken from ISIL elsewhere have stoked local fears and, given close ties to Iran, their advance has sparked warnings of a possible intervention from Tehran's regional rival Turkey.
Turkish President Recep Tayyip Erdogan has said Ankara will respond if the militias "cause terror" in Tal Afar.
Iraqi Prime Minister Haider al-Abadi tried to allay fears of ethnic and sectarian killings in Tal Afar, saying that any force sent to recapture it would reflect the city's diversity.
A Mosul resident said air strikes had intensified on the western part of the city, which is divided by the Tigris river running through its centre. The strikes seemed to be targeting an industrial area.
ISIL has dug in among more than a million civilians as a defence tactic to hamper the air strikes. They are moving around the city through tunnels, driving suicide car bombs into advancing troops, and hitting them with sniper and mortar fire.
READ MORE: Thousands of Iraqis fleeing Mosul 'cross into Syria'
Nearly 69,000 people have been displaced because of the fighting, moving from villages and towns around the city to government-held areas, according to United Nations estimates.
The figure does not include the thousands of people rounded up in villages around Mosul and forced to accompany ISIL fighters as human shields as they retreat towards the city's centre.
Source: News Agencies