ISIS Quashes Mosul Rebellion That Aimed to Give City Back to Baghdad By Drowning Dissenters

Updated | The Islamic State militant group (ISIS) quashed a rebellion in the northern Iraqi city of Mosul, just days before a U.S.-Iraqi offensive began on Monday. The group executed 58 people by drowning and burying them in a mass grave, according to Iraqi officials and residents.

The plot was spearheaded by an ISIS commander who wished to defect from the group and help Baghdad recapture the city, which ISIS took control of in June 2014, Reuters reported residents as saying. They said by phone that ISIS buried the bodies of the suspected plotters on the outskirts of the city.

The commander in question was a key aide to ISIS's self-proclaimed leader Abu Bakr al-Baghdadi, according to accounts that five residents, Hisham al-Hashimi, adviser to the Iraqi government on ISIS, and an Iraqi colonel, gave to Reuters. His identity has been withheld to protect the security of his family.

Hashimi told Reuters that ISIS detained the plot suspects after discovering a message on one man's phone that spoke of a weapons transfer. Under interrogation, the suspect admitted that weapons were being stored in three different areas of Mosul, to be used in a rebellion against the city's rulers.

In recent months, ISIS militants in Mosul have increasingly released footage of executions of those accused of spying or working against the group. It has tightened its grip on the residents of the city as it becomes increasingly fearful of losing its largest capture to date.

The plot and allegations of spying have increased the possibility of Mosul insiders aiding the ground offensive that Iraqi Prime Minister Haider al-Abadi announced on Monday. Some dissenters in Mosul have reportedly started to graffiti the letter M that stands for muqawama , which means resistance in Arabic, on the side of the walls of the property of ISIS militants to unnerve them.

The Iraqi government had made efforts to reach out to civilians inside the city to build support in the days leading up to the offensive. Earlier this month, Abadi made his first radio broadcast into Mosul, telling residents that they would be liberated from ISIS control soon. "We have liberated all major cities ISIS held in Salahideen and Anbar province and we will celebrate the big victory of Mosul with you soon," he said in the broadcast, before the Mosul offensive began.

"We will raise the flag of Iraq in the center of Mosul as we have raised it in al-Qayyara, Shirqat, Baiji, Tikrit, Ramadi, Fallujah and many other cities around Iraq which have been reunited with our home, Iraq, and our people."

The U.S.-led coalition is ramping up its airstrikes on ISIS positions in the city and the surrounding region, while Iraqi and Kurdish forces are leading the ground operation. The city is believed to still hold a population of more than 1 million people, mostly Sunni Arabs, and humanitarian groups have warned of a major crisis with 700,000 Mosul residents likely needing assistance as the operation progresses.

The city remains ISIS's biggest prize, despite a series of territorial losses in Iraq and Syria. It is where ISIS's self-proclaimed leader Abu Bakr al-Baghdadi announced the creation of the group's caliphate straddling the Iraqi-Syrian border.

This article has been updated to reflect recent developments in Mosul.