A feared Turkish invasion of northeast Syria could spark a resurgence of the ISIS group, analysts and Kurdish forces have warned, despite Ankara's pledge to prevent the jihadists' return.
Ankara has threatened an offensive in Syria against Kurdish factions it considers terrorists and US forces on Monday pulled back from Turkish border areas, opening the way for an invasion President Recep Tayyip Erdogan has said could come at any moment.
An open assault would reverse years of successful Kurdish-led operations to defeat ISIS and allow some of its surviving leaders to come out of hiding, said the Syrian Democratic Forces (SDF), the Kurdish faction that controls much of northeastern Syria.
With little other leverage left in the regional game, Sam Heller of the International Crisis Group think tank, told AFP the SDF has an "interest" in warning of an ISIS threat if open conflict breaks out with rival Turkey.
"But the fact is that ISIS is still a threat, one that seems likely to metastasize if the SDF is forced to divert attention and resources... to a defensive battle against Turkey," he said.
While a Kurdish-led operation earlier this year saw the death of ISIS’ territorial caliphate, the organization isn't dead and sleeper cells have been active in SDF-held areas and in Syria's vast desert where they continue to hit regime forces with deadly attacks and ambushes.
Charles Lister, director of the US-based Middle East Institute, said US President Donald Trump was "granting ISIS the gift of rebirth".
The US military itself has warned that, short of sustained international pressure, ISIS would soon have the ability to regroup.
"The battle against ISIS is not over," Abdulkarim Omar, the top Kurdish foreign affairs official, told AFP Monday. “There are hundreds of sleeper cells in recently liberated areas.”
Camps and detention centers
The SDF, with backing from the US-led coalition, has scored major victories against ISIS near the Turkish border in Kobane and in the extremists' former Syria capital of Raqqa.
This year, they declared the territorial defeat of the group after seizing Baghouz, the final ISIS bastion in eastern Syria.
The SDF is now concerned that extremists could replenish their ranks by freeing thousands of fighters and their families who are being held in detention centers and informal settlements in Syria's northeast.
The Kurds consistently warned that they would be unable to guard ISIS fighters if their forces were busy fighting off a Turkish offensive.
On Monday, Omar said that detention centers are not heavily fortified.
"They are only buildings... in the event of any security vacuum, these criminals could have an opportunity to break free," he said.
The official also said he was concerned about displacement camps, namely Al-Hol, the largest of the settlements, which he described as a "time bomb".
Security incidents have been on the rise in the crowded camp, which houses more than 3,000 ISIS families among its more than 70,000 residents, according to the Kurdish administration in northeast Syria.
The thousands of foreign ISIS brides held in Al-Hol, are "as dangerous as the thousands of ISIS fighters being held in SDF detention centers", it said this week, noting daily stabbings, killings and attempts to break free.
ISIS chief Abu Bakr al-Baghdadi has urged followers to free detained extremists and family members held at camps in Iraq and Syria, vowing "revenge" in an audio recording released on September 16.
SDF spokesman Mustefa Bali last month said ISIS militants "have stepped up their regrouping efforts through women in the camp recently".
The Institute for the Study of War last week said ISIS is bribing prison guards and raising funds to smuggle women out of camps, including Al-Hol.
"ISIS is likely preparing more coordinated and sophisticated operations to free its detained members," it said in a report citing incidents in which prisoners and ISIS brides managed to break free.
Turkey, however, assured Monday that it "would not allow ISIS to return in any shape and form".
But analysts argue that Ankara could unintentionally help boost extremists.
"Turkey will not intentionally target camps and prisons but it could inadvertently strike them in the process of intervention," Syria expert Samuel Ramani told AFP.
Heller also said a direct Turkish attack on camps and prisons was unlikely.
"What seems more likely is that these facilities, which are already vulnerable to riots and attempted jailbreaks, will be left vulnerable as the SDF redeploys the forces securing them to fight Turkey," he said.
"If ISIS cadres escape in the ensuing chaos, they could catalyze ISIS operations locally. Or, if they flee the Syrian battlefield, they could augment militant groups internationally."