A Sunni insurgency is taking root in Iraq as the U.S.-led coalition continues to weaken the Islamic State's territorial strongholds, particularly in Mosul, according to a new report.

The D.C.-based Institute for the Study of War warned that al Qaeda's top leadership likely will capitalize on ISIS's continued losses and attempt to gain influence within splinter militant groups opposed to the Shia-led government of Iraq.

Emily Anagnostos, the researcher who authored the report, told the Washington Free Beacon on Wednesday that the U.S.-led coalition fighting ISIS in Iraq and Syria needs to broaden its focus to target smaller Sunni insurgent groups that likely will grow as ISIS faces setbacks.

"Now that we're putting pressure on ISIS, ISIS is taking its foot off of these groups and allowing them to grow," Anagnostos said. "We're seeing early signs that these groups are operating in Iraq and could ultimately project a threat to the West, as ISIS does today."

ISIS's partial withdrawal from eastern Mosul already has created an opportunity for the Naqshbandi Army, or JRTN, a U.S.-designated terrorist organization led by high-ranking members of the Saddam Hussein-era Arab Socialist Ba'ath Party. The report predicted that JRTN would reemerge in the "vulnerable period" after ISIS loses control of the city but before the Iraqi government regains full control.

Al Qaeda has remained active in Iraq the past three years despite being overshadowed by ISIS. Al Qaeda leader Ayman al Zawahiri in August urged its Syrian branch to rebuild alliances in Iraq and resume a "long guerrilla warfare." As recently as Jan. 31, local police arrested two militants in central Iraq who conceded they had ties to al Qaeda.

ISW cited two incidents in December 2016 where clusters of improvised explosive devices (IEDs) were detonated in neighborhoods outside of Baghdad. ISIS claimed responsibility for one of the attacks but remained silent about the other. ISW noted it is extremely rare for ISIS to carry out clustered IED attacks, evidence that a group separate from ISIS may have carried out one or both of the attacks.

Al Qaeda threatens to undermine Iraq's electoral process, particularly on the local level. The report warned that al Qaeda and splinter groups likely would carry out attacks at campaign rallies and voting stations this year as Iraqis vote during the nation's fourth round of provincial and parliamentary elections.

The top U.S. commander in Iraq said Wednesday that ISIS could be fully driven from Mosul in the next six months.

While military efforts to defeat ISIS would bring short-term success, Anagnostos recommended the Trump administration focus on long-term solutions such as assisting the Iraqi government to create a political environment that fully includes Sunnis. She said a political solution would offer Sunni Arabs a means to confront the Iraqi government through peaceful avenues rather than extremism.

"We want to set conditions in Iraq where it has a fully functioning government," Anagnostos said. "You need to establish a country that a Sunni insurgency can't destabilize, otherwise there will be grounds that allow for the growth of insurgency groups that can become existential threats to the U.S."

She added that the Trump administration should assume a larger role in reconstruction efforts to rebuild destroyed cities and assist in humanitarian efforts at internally displaced person camps.

The report noted that refugee camps are especially vulnerable to insurgent recruitment efforts.