This article is from the archive of our partner .

The bodies of 12 men were found in the Iraqi town of Saadiya, north of Baghdad on Monday, as infighting between Sunni insurgents intensifies and threatens the Islamic State's advancement on Baghdad.

The killings, which appeared to be executions, represent a growing divide between ISIS and other Sunni insurgents, particularly the Naqshbandi Army, a group believed to be led by former Sadam Hussein deputy Ezzat Ibrahim al-Douri, the only top member of the dictator's entourage that has not yet been captured or killed since the U.S invasion in 2003.

Local residents who discovered the bodies confirmed they were Naqshbandi fighters, and blamed ISIS for the killings, according to reporting from ABC News.

The Islamic State relied heavily on support from Sunnis hoping to overthrow Prime Minister Nourial Maliki's Shiite government during their initial offensive in June. With the help of the Naqshbandi Army, ISIS overran northern cities and vowed to continue on towards Baghdad to establish a true Islamic State. Saadiya was overrun on June 10, the same day as Mosul, one of Iraq's largest cities.

Tensions quickly rose when more moderate Sunnis clashed with ISIS over the Al-Qaeda offshoot's strict interpretation of Islam and rejection of national borders.

Ahmad al-Zarghosi, a local government official who fled Saadiya, told Reuters he estimates that 90 percent of the population has moved north since fighting broke out between the Naqshbandi Army and Islamic State militants earlier in the week.

Iraq's national army had been fighting the Islamic State over control of the nearby city of Sadur, which a Maliki spokesman said the army had retaken on Sunday.

This article is from the archive of our partner The Wire.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.