Baghdad: An Iraqi militia said on Wednesday it was on the verge of driving IS fighters from an air base west of Mosul, a victory which would threaten the group's supply route from Syria to its last major stronghold in Iraq.
Some IS fighters have already pulled out of the Tal Afar base and moved to the town of the same name, said Jafaar Hussaini, a spokesman for Kata'ib Hezbollah group.
Should Kata'ib Hezbollah succeed, it would be a significant development in the campaign to recapture Mosul, IS's de facto capital since its forces swept through Iraq in 2014.
The base lies about 60 km (38 miles) west of Mosul on the main road to Syria and its recapture would endanger IS's supply route for Mosul.
But the development could also alarm Turkey, which is wary of involvement in the civil war in Syria.
Kata'ib Hezbollah is a main component of the Popular Mobilisation, a coalition of mainly militias taking part in the battle for Mosul.
While the coalition is fighting IS west of Mosul, regular army and police units are trying to advance from the other sides, backed by Kurdish Peshmerga fighters deployed in the north and the east.
Iraqi counter-terrorism forces breached IS defences in east Mosul two weeks ago but have faced resistance from the militants, who have fought back with suicide car bombs, snipers and waves of counter-attacks.
The campaign that began on October 17 with air and ground support from a US-led coalition is the biggest military operation in Iraq in more than a decade of turmoil unleashed by the 2003 invasion that toppled Saddam Hussein.
Popular Mobilisation, known locally by its Arabic name Hashid Shaabi, has said it plans to use Tal Afar base to take the battle against IS into Syria.
The government forces have been fighting in a dozen of the roughly 60 neighbourhoods on the eastern part of Mosul, which is divided by the Tigris River. They have yet to enter from the northern and the southern sides.
Iraqi officials say the militants have used the city's more than one million remaining residents as human shields, firing from rooftops of inhabited houses and using a network of tunnels to launch ambushes in the midst of residential areas.
While the presence of civilians has slowed the advance, Iraqi officials say some of their operations have been assisted by information provided by residents about IS military positions.
Trying to stop the flow of any information out of Mosul, the militants have cracked down on communications, banning the use of mobile phones and also confiscating satellite dishes to prevent people from seeing the progress made by Iraqi forces.
The group has also killed civilians suspected of helping the attacking forces, sometime putting their bodies on display around the city.
Iraqi military estimates put the number of IS fighters in the city at 5,000 to 6,000. Facing them is a 100,000-strong coalition of Iraqi government forces, Kurdish fighters and paramilitary units.
Iraqi authorities have not published a casualty toll for the campaign overall - either for security forces, civilians or IS fighters. The warring sides claim to have inflicted hundreds of casualties in enemy ranks.
Nearly 57,000 people have been displaced because of the fighting from villages and towns around the city to government-held areas, according to UN estimates.
The figure does not include the tens of thousands of people rounded up in villages around Mosul and forced to accompany IS fighters to cover their retreat towards the city.