The Pentagon has made its centerpiece of its strategy in Iraq arming Anbar Sunni tribes to convince them to back the Shi’ite-dominated government. That plan has been stalled by the government blocking most of the arms transfers, and with sectarian tensions on the rise, it looks like some of those tribes are going the other way.

Today, key Anbar sheikh Ahmed Jumaili read a joint statement from a number of key tribes in Fallujah, pledging loyalty to ISIS, and expressing their belief that the best way to return calm to the province was by backing ISIS against the “infidels, apostates and Shias.”

ISIS has struggled with its relationship with tribes in Anbar as well, getting into some fairly ugly battles around the city of Hit, which ended with them purging certain tribes they perceived as too “pro Baghdad.” Where they have managed to keep the tribes placated in both Iraq and Syria, they have enjoyed the most success.

The Iraqi government’s decision to put Shi’ite militias on the front lines in Sunni territory has been extremely contentious. The Iraqi military has clearly been unsuccessful without them doing the heavy lifting, but ugly crackdowns by the militias on Sunni locals has fueled unrest, and seems to be a key part of bringing many to see ISIS as the safer choice.

How long this lasts remains to be seen, but tribal leaders in some parts of Anbar were practically in open revolt before ISIS started taking over cities, meaning the split when ISIS moved in was much easier for people to swallow.