Iraqi militia fighters peered from a front line position at Tal Afar, a town still held by jihadists, as sniper bullets rang overhead and mortar rounds crashed nearby.

After storming a former airbase, they have pushed forward to around four kilometres from the strategic town, 55 kilometres (35 miles) west along the road running from the Islamic State group's bastion of Mosul to territory under its control in Syria.

"God willing, we are going to advance forward!" field commander Abu Hanan al-Kanaani said. "The enemy knows us, nothing will stop us and we are coming to liberate, to let the people live in freedom and safety."

The push by the Hashed al-Shaabi (Popular Mobilisation) forces -- a paramilitary umbrella group dominated by Tehran-backed Shiite militias and nominally under the Iraqi prime minister's command -- is part of the broader offensive to retake Mosul, IS's last major hub in Iraq.

But while the forces' thrust should be a vital move to cut off IS escape routes, its involvement around Sunni-majority Mosul and its targeting of Tal Afar have proved deeply divisive.

Alleged executions and abuses carried out by Hashed fighters in territory taken from IS elsewhere have stoked local fears and, given its close ties to Iran, its advance has sparked warnings of a possible intervention from Tehran's regional rival Turkey.

On the battlefield, however, the group is bullish after recapturing what was once a major Iraqi military facility that IS fighters seized as they swept through the country in 2014.

On Sunday, the paramilitary group drove a group of Western journalists six hours on a press trip through the desert to showcase the capture of the airbase.

"Daesh sent several car bombs at us but when they saw we would not back off, they fled," representative Mohammed al-Barghuthi told AFP, using an Arabic acronym for IS. "It took us about an hour to capture."

- Regional game -

Now the group has Tal Afar firmly in its sights and is waiting for orders to move.

"We are waiting to tighten our grip around the city and trying to secure a route for the civilians to leave," said Abu Mohamed al-Ettabi, a senior commander on the Tal Afar front.

The likely capture of Tal Afar -- a mainly Turkmen city -- by the Popular Mobilisation has drawn the ire of the president of Sunni neighbour Turkey, Recep Tayyip Erdogan.

He cautioned that Ankara -- which has some hundreds of soldiers based at Bashiqa, north of Mosul, and more along the borders -- would "not look favourably" on an attack by Shiite militias on the town.

Ettabi said the plan was for local units from the area fighting under the banner of the Popular Mobilisation force to try to move into the city.

"But if they cannot make it, then we are going to intervene," he said.

He dismissed the potential threat of Turkish military action if the militias take the town.

"Turkey is not Iraq -- they can't impose what they want on us," the senior commander said. "Iraq will decide what it wants and no one can interfere."

The role played by the Hashed remains a potential flashpoint and the group -- which includes US terror-listed organisations -- is not receiving air support from the US-led coalition fighting IS.

But Ettabi angrily lashed out at suggestions the group was part of a plan by Iran to carve out a corridor of control to neighbouring Syria, where it is fighting to prop up President Bashar al-Assad.

"Let's stay far away from these political plots and focus on the issue that our population has been attacked," he said.