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Currently a sideshow compared with the street-to-street fighting in Mosul, some 70 kilometers (44 miles) to the east, the battle for Tal Afar is certain to boost Shiite power. And its significance could be just as great -- if not greater -- for Iraq and the future of the region than the main battle for Mosul itself.

Officially, the Iraqi government and top militia leadership say that only Iraqi army units will enter Tal Afar, once dominated by Shiites but now primarily Sunni Turkmen, a minority in the country with cultural and historic links to nearby Turkey to the north.

But some of the militias' most powerful units, as well as field commanders and troops -- all backed by a newly empowered Iran -- tell a different story.

Jaafar al-Husseini, spokesman for Iraq's Hezbollah Brigades, said it is the militias backed by Shiite-heavy army units and Iranian weapons that will lead the charge into Tal Afar to drive out IS extremists.

"The Iranians are with us," he said, adding that Tehran was supporting the militias directly, including strategy from Revolutionary Guards commander Gen. Qassem Soleimani, who is in charge of a crescent of Shiite power stretching from Tehran to Beirut.

"Our mission and that of the (Iraqi Shiite) Badr Brigades is to encircle Tal Afar from the east. Then we will storm it," he said, adding that Soleimani visited a nearby staging ground three days ago.

Iraq's Shiite militias mobilized against IS in 2014. Since then, they have shown a growing determination to be a major force shaping the country.

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