Tensions have been mounting over the past year or so as al Qaida-linked groups have been bolstered by a flood of thousands of foreign fighters with significant amounts of experience, funding and equipment. Many Syrians resent the presence of the foreign forces.
"ISIS is determined to irritate every faction of the insurgency," said Will McCants, an expert on Islamist militants at the Brookings Institution, a research center in Washington. Drawing a comparison to Iraq, where ham-fisted rule by the Islamic States predecessor, al Qaida in Iraq, led to a rebellion among Sunni Muslim tribal leaders that ultimately drove al Qaida in Iraq from the areas it controlled, McCants noted that it seems like they learned nothing.
Tamimi agreed that the Islamic States moves were alienating former allies. Its clear that ISIS has lost favor among many previous sympathizers in Azaz, he said. For example, one local outlet, Ahrar Azaz, features the ISIS flag on its Facebook page but is now criticizing ISIS over its conduct in the town.
There are no firm numbers on al Qaida sympathizers among Syrias estimated 100,000 rebels. A study released this week by Charles Lister, an analyst with the defense consultancy IHS Janes in Great Britain, said 10,000 to 12,000 were members of the Islamic State and the Nusra Front but that perhaps another 30,000 hard-line Islamists coordinated their military actions with them.
But its difficult to pin down the beliefs of the estimated 1,000 organizations that make up the anti-Assad rebel movement. The main group that fought the Islamic State in Azaz, the Northern Storm Brigades, has admitted to kidnapping and holding nine Lebanese Shiite Muslim pilgrims for more than a year, robbing and shaking down local merchants in the name of the revolution and conducting sectarian attacks on religious minorities in northern Syria.