A report released by a U.S.-based think tank estimated that the attacks were carried out by a small number of ISIS fighters operating in Iraq. The report, issued by the Newlines Institute in May, said that groups of 350 to 400 ISIS fighters were concentrated in five areas north and west of Baghdad, including 50 to 100 fighters operating in urban centers in Anbar, Salah ad Din, Diyala, Kirkuk, Ninewa, and Baghdad provinces. CJTF-OIR reported that its estimates of the number of ISIS fighters in Iraq are classified.
CJTF-OIR reported that beyond ISIS’s ability to “skillfully” exploit Diyala’s physical terrain, the group exploits the large security “seam”—the area of the disputed territory where neither the ISF nor the Kurdish Peshmerga are capable of enforcing security—that runs through Diyala and other northern Iraqi provinces. A study published by the Combating Terrorism Center at West Point assessed that ISIS is able to find sanctuary in the security gaps and deserted villages between Kurdish and ISF troops in Diyala, which in some places can be 5 to 10 miles wide and 40 to 60 miles long. Both the Combating Terrorism Center study and a report by the Newlines Institute note that ISIS actively seeks to keep these rural areas depopulated to enable freedom of movement, evade informants, and stage for attacks on weaker local forces.
Read the full report here.