Counterterrorism specialists said the new study illuminates a trend that has been emerging for several months, as American-backed ground forces in Iraq and Syria have steadily rolled back territorial gains the Islamic State achieved in 2014 and used as the basis for its global appeal to Muslims to come join the caliphate. Now, its strongholds of Mosul, Iraq, and Raqqa, Syria, its self-declared capital, are besieged, and senior leaders have fled as opposing forces close in.
“ISIS has anticipated the loss of its government for over a year,” said William McCants, a senior fellow at the Brookings Institution and the author of “The ISIS Apocalypse: The History, Strategy and Doomsday Vision of the Islamic State.” “They are prepared to wage a war from the shadows to reclaim it.”
The report’s authors, Daniel Milton and Muhammad al-Ubaydi, say their findings aim to draw a more accurate picture of the military challenges in Iraq and Syria, especially in maintaining security in cities large and small that have been reclaimed from the Islamic State.
“Despite all of these positive connotations, the liberation of cities in Iraq and Syria has proved to be much more of a mixed bag for those living in the aftermath,” the report said. “Part of this is the challenge of governing post-liberation areas where city infrastructure has been destroyed and where security threats still remain.”
The report cites the example of Falluja, which was freed by Iraqi forces in June 2016. Many months later, news media reports suggest that residents still face an array of challenges, such as destroyed buildings, live Islamic State munitions buried in the rubble and the continuing threat of Islamic State attacks, the report said. In March 2017, the mayor of Falluja was still living in Erbil, a city in Iraqi Kurdistan in northern Iraq, and traveling to Falluja only on certain days for work.
The report draws on Islamic State claims that it carried out 1,468 attacks in 16 cities — 11 in Iraq and five in Syria — from the time insurgents were driven out of those cities until April.
In some cases, violence dropped off sharply once the militants were routed, with the Islamic State either unwilling or uninterested in carrying out harassing attacks ranging from small-arms ambushes to suicide attacks. But in other cities, the threat of violence remains pervasive.
The eastern part of Mosul, in northern Iraq, has had the highest number of attacks per month, 130, since Iraqi forces drove out Islamic State fighters. Baiji, Iraq, has the second-highest number of monthly attacks, at 21.
Islamic State fighters have employed a variety of tactics against cities they once controlled. Attacks that occur from a distance, employing weapons such as rockets and sniper rifles, were used in 56 percent of all strikes, while suicide bombings were used in only about 5 percent of operations, the report found.
In the western Iraqi city of Ramadi, the Islamic State used a large number of improvised explosives, particularly those called “sticky” bombs because assailants usually attached them to a car or truck using adhesive.
Suicide operations, while less common over all, have been used consistently to terrorize cities after they were freed from Islamic State control. But the relative difficulty of preparing and carrying out such attacks, including finding makeshift armor and retrofitting vehicles with it and building bombs, still makes them a selective weapon of choice.
“More complex suicide bombings, particular those involving vehicles, cannot be assembled on the spot,” the report concluded.
Insurgent activity in cities after the Islamic State’s defeats varies in the two countries (more in Iraq than in Syria), with researchers suggesting a correlation between proximity of the liberated city to the front lines. For instance, Ramadi is 32 miles closer to Islamic State territory than Falluja. Falluja’s average number of monthly attacks is just over one, while Ramadi’s is nearly 11, the report found.
Researchers also found that the Islamic State maintained the resources and expertise to carry out strikes against areas in which it was defeated, but seemed focused on avoiding operations that would exhaust its strengths in those areas, and on its ability to fight there in the future.
Enduring security, however, has not guaranteed political reconciliation. “Even in locations where the Islamic State is driven out and relative peace is restored, difficult political challenges remain,” the report said.
In March in Manbij, Syria, the report noted, United States forces intentionally drove through the streets of the city to prevent fighting between the two American allies — the Turkish Army and the Arab and Kurdish fighters that made up the so-called Syrian Democratic Forces.