As the U.S. prepares to withdraw its troops from Iraq by September 30, concerns are rising that ISIS may exploit the resulting security vacuum, according to counterterrorism expert Dr. Omar Mohammed.
ISIS fighters in Syria may have increased from approximately 2,000 to as many as 10,000 as the United States approaches its deadline for troop withdrawal from Iraq, a regional security expert warned on Sunday.
Dr. Omar Mohammed, a counterterrorism expert and researcher with the George Washington University Program on Extremism, expressed concerns about the potential for the Islamic State to take advantage of a security vacuum as U.S. forces prepare to leave by September 30. He noted that Iraq could be entering a perilous period, reminiscent of the time when ISIS seized Mosul in 2014.
“ISIS is waiting actively in the gaps, as it historically always has,” Mohammed told Fox News Digital. He emphasized that the critical issue is not whether American forces will leave Iraq on schedule, but rather what will remain in their absence.
Mohammed explained that Iran-backed militias often cite the ISIS threat to justify maintaining their weapons, while ISIS capitalizes on the grievances created by these militias to recruit new members. This dynamic, he noted, is similar to what led to the deterioration of security in Mosul before 2014, when the city found itself caught between a sectarian security apparatus and the insurgency it fueled.
In the years leading up to its capture of Mosul, ISIS developed underground networks through methods such as assassinations, extortion, intimidation, and infiltration. The group seized U.S.-made weapons and amassed hundreds of millions of dollars before its leader, Abu Bakr al-Baghdadi, declared the establishment of a self-proclaimed caliphate.
During that time, Mohammed launched “Mosul Eye,” a blog that documented life under ISIS rule, revealing the group’s operations and providing intelligence to U.S. forces. Iraqi forces, supported by the U.S.-led coalition, eventually recaptured Mosul in July 2017. However, even after the end of the U.S. combat mission in 2021, ISIS has continued to operate in various regions of Iraq and Syria.
U.S. Central Command (CENTCOM) has stated its commitment to dismantling ISIS networks and preventing the group’s resurgence. Nevertheless, Dr. Mohammed cited Iraqi intelligence estimates indicating that the number of ISIS fighters in Syria has surged since the collapse of Bashar Assad’s government in 2024.
He also pointed out that the Popular Mobilization Forces (PMF), an umbrella organization integrated into Iraq’s security forces, was never disbanded following ISIS’s territorial defeat. Mohammed estimated that the PMF comprises around 238,000 members, receives billions in government funding, and includes factions with close ties to Iran that operate outside the Iraqi government’s direct control.
As Baghdad attempts to bring armed factions, including Kataib Hezbollah and Asaib Ahl al-Haq, under full state control, Mohammed remarked, “September 30 is not one deadline; it is two,” referring to the simultaneous U.S. withdrawal and the domestic disarmament initiative.
He emphasized that the militias and ISIS are not separate entities but are deeply interdependent, each justifying the existence of the other. Both groups thrive in the unstable environments that the central government struggles to maintain.
The U.S. withdrawal aligns with a 2024 U.S.-Iraq agreement that aims to conclude the mission in Iraq by 2025 while continuing support for anti-ISIS operations in Syria through September 2026. Mohammed cautioned against repeating past complacency, stating, “Mosul did not fall in 2014 because ISIS was strong. It fell because everything that would have detected its strength—presence, attention, honest reporting from the ground—had been withdrawn in the years before, while the world’s eyes were elsewhere.”
Meanwhile, Iraqi Prime Minister Ali al-Zaidi’s meeting with the White House on July 14, during which it was announced that remaining U.S. troops would leave Iraq, faced condemnation from Tehran. According to Iran International, Ali Akbar Velayati, an adviser to Iran’s Supreme Leader Mojtaba Khamenei, criticized al-Zaidi’s trip as “regrettable” and claimed it undermined Iraq’s dignity.
Dr. Mohammed noted that Iran’s influence in Iraq is particularly significant now, as U.S. strikes have weakened parts of its proxy network. He stated, “Iran’s strategic calculation matters more now than at any point in a decade because Iraq is essentially what Iran has left.” He warned that Tehran’s real fear is not the resurgence of ISIS but rather becoming irrelevant.
Tehran is concerned about a scenario in which the Iraqi government successfully disarms militias, U.S. forces withdraw on Baghdad’s terms rather than Iran’s, and no active security crisis remains to justify armed groups operating outside of full state control.
Dr. Mohammed concluded by asserting that the future of the region after September will not be determined solely by stated intentions or diplomatic promises. “I have seen what a city pays when that judgment is wrong,” he warned. “Whether ISIS grows large enough to frighten Iran or stays just large enough to serve it will be one of the defining questions of the year following the withdrawal,” he said.
Fox News Digital has reached out to the White House for comment.