The Hashed Al Shaabi have trained their weapons on Tal Afar and besieged the town for nearly a year, but their role in taking the town has yet been clearly defined, writes Florian Neuhof
The battle for Tal Afar and why Shiite militias are involved
As has become tradition in Iraq's long fightback against the self-proclaimed Islamic State, the battle to retake the town of Tal Afar commenced on a Sunday.
A dusty town in the remote desert plains near the Syrian border, Tal Afar is one of the last strongholds of the terror group in Iraq. Its jihadist defenders had been sitting uncomfortably as Iraqi forces slowly ground down resistance in ISIL-held Mosul over the past year.
Between October 2016 and July this year, government forces gradually clawed back Mosul from the insurgents, routinely beginning each of the many stages in the massive operations on a Sunday, the first day of the week in Iraq.
As the Iraqi military was decimated in the brutal fighting in Mosul, the country's second largest city, others took care of business in Tal Afar - some 60 kilometres west of Mosul.
Shiite militia groups, known as the Hashed Al Shaabi or the Popular Mobilisation Forces, drove west in long columns of sand-coloured vintage pickup tricks and mounted anti-aircraft cannon on their flatbeds.
The Hashed initially insisted they would be taking part in the battle for Mosul, but were eventually dissuaded by the government.
They begrudgingly obliged, and instead trained their guns on Tal Afar, the most important town in the stretch of desert between Mosul and the Syrian border. Soon, the route between Syria and Mosul was cut, and Tal Afar surrounded by the Hashed.
The militia advance ensured that Mosul was surrounded from all sides, preventing ISIL from sending more men and material into the city.
It also meant the extremists defending Mosul were trapped. In a war in which surrender usually meant a bullet through the back of the head, they now had few options but to fight to the bitter end.
In private, battlefield commanders complained about the move, and the fierce resistance by thousands of trapped extremists took a heavy toll on the elite counter-terrorism troops leading the charge. It is not known why Iraq's top brass decided on cutting all escape routes from Mosul.
Iraqi prime minister Haider Al Abadi, the commander-in-chief who does not enjoy a reputation as a competent strategist amongst the military, might be behind it.
But there is also speculation that the Hashed acted on their own accord, driven by strategic considerations of another kind.
Many of the disparate Shiite militia groups are not just trained and equipped by Iran, they are also beholden to Tehran - a regional actor that projects influence into Iraq and beyond.
Iran is heavily involved in propping up the Assad regime in Syria, and had little interest in ISIL fighters escaping Mosul to fight another day across the border. Could the Hashed have acted unilaterally against the interests of the Iraqi government?
In the run-up to the Tal Afar operation launched this week, the Hashed had been equally verbose about joining the fight. No doubt the rank and file are keen to get involved after besieging the town for almost a year.
Tal Afar has long been a hotbed of violent Sunni extremism, first harbouring Al Qaeda and then ISIL, and taking the town holds symbolic as well as practical value.
But there is as yet no clarity to what extent the militias will be involved, and which groups will be on the frontlines.
The Hashed are divided into units that existed prior to the rise of ISIL, and which have close ties to Tehran, and units that formed in response to the extremist threat in 2014, which are closer to Baghdad.
For the militia groups aligned with Iran, Tal Afar has already lost some of its strategic value. One of the key aims of the Hashed has been the creation of a land corridor connecting Iran with Syria, and that goal was achieved when its fighters pushed ISIL out of the southern plains of the Sinjar area in May.
The Hashed do not need to hold Tal Afar for men and material to travel all the way through Iraq in areas under their control.
And, for all their bluster, there are good reasons to stay out of the fight.
Official estimates put the number of ISIL combatants at a thousand at a minimum. They are fighting from well-prepared positions and will inflict heavy losses with their tactics of deploying suicide car bombs, explosive booby traps and snipers.
Why lose militiamen when the Iraqi military could suffer instead? A further weakening of the elite counter-terrorism troops in particular would play into the hands of the Hashed, who are vying for control over Iraq at the expense of the government.
To the 10,000 to 50,000 Sunni civilians believed to be trapped in Tal Afar, an omission of the Hashed might sound like good news. The Shiite militias have committed war crimes in most - if not all - the battles they were involved in, killing civilians as well as ISIL prisoners.
It may well not matter. In the final weeks of the battle for Mosul, Iraqi forces executed scores of civilians, believing all those still left alive to be ISIL members. It is unlikely they will see the remaining inhabitants of Tal Afar in a different light.