ISTANBUL -- Sunni tribesmen in Iraq's volatile Anbar province appear set for a critical test in the fight against the Islamic State group. As the Iraqi army generally stays out of the large western province, focusing instead on fighting the Islamic State in Tikrit, local militias and police are taking up the bulk of the operations – and they are coming under increased pressure from militants, without much support from Baghdad's army.

The police in Anbar, a Sunni-majority province, are leading the fight against the group also known as ISIS or ISIL by recruiting locals to fight on the front lines. Anbar is a major battleground in the war against the terrorist group, but instead of the Iraqi military taking charge, the local tribes are largely left to run the fight themselves, because of sectarian mistrust.

The Sunni brigades have restricted access to the battlefield, to keep out the Iranian-backed Shiite militias making progress against ISIS elsewhere in Iraq, as well as Shiite regular soldiers. So they are heading into battle almost entirely on their own. Long-standing distrust between the tribes and the Shiite-dominated military prevents the two from working together, tribal leaders said in interviews, although there have been cases of successful cooperation.

The only current Iraqi military presence in Ramadi, the largest city in Anbar, are a few dozen Sunni soldiers, some of whom are veterans who fought during the “Sunni Awakening” in 2007, when Sunnis were recruited by the U.S. to fight in local militias against al Qaeda.

Anbar police are forming brigades of volunteers, only some of whom have battle experience, from across the province, Sunni tribesmen fighting with the new brigades said in interviews. The men selected to fight in the brigades completed a monthlong training course at a military academy in Anbar and are being equipped with weapons stolen from ISIS, or in some cases provided by the Baghdad government.  

Anbar province, particularly in places like Ramadi, is one of the only places in Iraq where the police force is now not only patrolling the streets for security but also acting as the military and the government.

Last week ISIS detonated several car bombs in Ramadi, killing dozens of civilians and signaling an effort to push into the province, which would put them closer to Baghdad. If ISIS took Anbar, that would create a direct route from the core region of its so-called caliphate in Syria to the Iraqi capital. Since the beginning of February, the Sunni tribes have attempted to stop the militant group from advancing in the region and from reaching the Ain al-Asad air base, where U.S. personnel are stationed to help train Iraqi forces.

The situation in Ramadi will likely only grow worse, tribal leaders said, because the militant group is focusing on Anbar, as well as on some parts of Iraqi Kurdistan near Kirkuk.

Tribal leaders also said they have not yet received any shipments of weapons promised by the U.S., meaning they will have to fight with the limited arsenal they received from the Iraqi army and whatever they can scavenge from defeated ISIS units.