Residents of Iraq's second-largest city, which has been under the control of ISIS since early June, have reportedly started clashing with militants, Tim Arango reports for The New York Times.

They're chafing under the brutal rule of an organization too extreme even for Al Qaeda. But ISIS's assault on the region's cultural heritage has been particular cause for local alienation from the group.

The residents of Mosul started to react negatively to ISIS' rule in the city after the militants razed a tomb that was thought to have contained the remains of the prophet Jonah. Jonah is revered in the Jewish, Christian, and Muslim faiths, and the tomb was one of the city's icons.

So far, resistance to ISIS's drive to destroy historic sites in the city — with almost 24 marked for demolition — has been patchy but nevertheless noticeable. A mass of citizens confronted ISIS fighters as they attempted to destroy the city's famed leaning minaret. According to witnesses, the landmark was saved.

Residents in Mosul are said to have formed armed gangs to counter ISIS. Bashar al-Kiki, the chairman of the Nineveh Provincial Council, of which Mosul is a part, told The Times that armed citizens had killed four ISIS militants.

“The people of Mosul are intensely angry at ISIS,” al-Kiki told The Times. “They can’t bear them anymore. This volcano of anger will explode soon.”

ISIS took Mosul on June 10 with extreme ease, as Iraqi Security Forces retreated — at times even stripping off their uniforms in hopes of evading capture by the group during its rapid advance. ISIS's seizure of Mosul was also enabled by former Baathist fighters who maintained a stronghold in the city.

ISIS and the Baathists are cooperating out of shared short-term interests, but ultimately the two groups hold diametrically opposed views on the future of Iraq and will most likely clash at some point.

There has already been sporadic fighting throughout Iraq between ISIS and Baathist fighters. The destruction of cultural heritage in Mosul and growing local frustration against the group could be another step in the complete breakdown of their alliance.