The US has stepped up its battle against Isis in Syria as it seeks to prevent the group exploiting a power vacuum after rebels toppled the Assad regime, launching some of its heaviest air strikes against the jihadis in years.
In the past two weeks, US forces have struck more than 75 Isis targets during two waves of attacks targeting jihadi leaders and camps in the fractured Arab state. They have killed at least 12 militants and bombed areas previously controlled by regime forces and Russia, one of ousted President Bashar al-Assad’s main foreign backers.
General Michael Kurilla, the head of the US’s Central Command, also visited northeastern Syria to meet American troops and the Syrian Democratic Forces, Washington’s main local ally in the fight against Isis.
The flurry of military activity, which began hours after Assad fled to Moscow as rebels seized Damascus on December 8, underscores US concerns that Isis will use the void created by the regime’s spectacular collapse to reconstitute.
“The single biggest risk I see is that Isis comes back because Isis wants to take advantage of any vacuum or instability in Syria following a civil war,” US national security adviser Jake Sullivan said on Thursday.
“I will not sugarcoat it,” he added. “This is a real threat — the threat of jihadism and terrorism returning in Syria, because of what’s happened. And it’s incumbent upon us and everyone in the region to push back hard on that.”
Syria was once part of Isis’s self-proclaimed “caliphate” and is home to several thousand jihadi fighters, prisons for captured militants and camps that house more than 40,000 Isis-related individuals and family members.
International coalitions have significantly weakened Isis since the jihadis launched a blitz across Iraq and Syria a decade ago and seized a swath of land about the size of Britain. The group was driven from its remaining territorial strongholds in 2019 and now operates in a network of cells, as well as through offshoots across Asia and Africa.
Centcom estimated in July that there were 2,500 Isis fighters across Syria and Iraq. In Syria, they have largely been restricted to pockets of central and eastern desert between territory that was controlled by the former regime and the US-backed SDF, which is dominated by Kurdish militants.
But the group has been more active this year. Centcom said the jihadis had claimed 153 attacks in the first half of the year and were “on pace to more than double” the total number from 2023, indicating that “Isis is attempting to reconstitute”.
Charles Lister at the Middle East Institute said in a report that the “reality is far worse” than Centcom’s statement suggested, as Isis only claims a fraction of its attacks in Syria and Iraq.
He added that Isis has conducted more complex attacks this year, including coordinated ambushes, targeted assassinations and assaults on oil and gas facilities, as well as checkpoints.
The battle against Isis now risks becoming more complex and precarious after Hayat Tahrir al-Sham led the rebel offensive that toppled Assad, with an alphabet soup of local factions and foreign powers seeing a window to pursue their own interests.
Turkey, the most influential foreign actor in post-Assad Syria, has said its “strategic goal” is to eliminate the Kurdish militant movement that dominates the SDF, which it considers an extension of Kurdish separatists that have fought the Turkish state for decades.
Ankara has thousands of troops deployed in northern Syria to push back against Kurdish militants and backs rebels under the umbrella of the Syrian National Army. The SNA, which co-ordinated with HTS during its offensive, has capitalised on the chaos to attack SDF territory.
This leaves the US, which has about 900 troops in Syria, trying to keep the peace between a Nato ally and the Syrian force it has armed and trained to fight the jihadis.
Experts say a significant risk would be if the Turkish-backed rebels attacked the SDF in Hasakah in northeastern Syria, where the Kurdish-led group runs detention facilities for about 9,000 Isis prisoners, including foreign jihadis.
In September, Kurilla described the prisons as “a literal and figurative Isis army in detention” warning that if a large number of militants escaped “it would pose an extreme danger to the region and beyond”.
Preventing break outs from prisons holding Isis fighters is “probably one of the most important things going forward to make sure everything is stable”, said Aaron Zelin, an expert on jihadism at The Washington Institute think-tank.
But, he added, “if the US makes sure nothing along those lines happens”, the Isis threat can be managed through American air strikes and ground operations.
Experts argued it will be in the interests of HTS, the country’s de facto rulers, to support the campaign against Isis.
HTS’s leader Abu Mohammed al-Jolani briefly fought with Isis in Iraq more than a decade ago but has since spent years fighting the group. He has sought to present HTS, a former al-Qaeda affiliate, as a more moderate force.
“HTS and Isis have been at each other’s throats for 11 and a half years, they hate each other,” Zelin said.
Jerome Drevon, an expert at the Crisis Group think-tank, said preventing an Isis resurgence will be vital to HTS’s efforts to project stability and gain legitimacy with international powers.
The US, UN and others have designated the group and Jolani, who has begun using his birth name Ahmed al-Sharea, as terrorists. But Washington and other western powers have started to communicate with HTS as they hope to support a peaceful transition in Syria with counterterrorism a priority.
Experts say HTS’s efforts to gain western backing means it is also more likely to want a deal with the SDF, which has tens of thousands of fighters, than a battle.
“HTS wants legitimacy, and the easiest way to gain it is to say we can fight terrorism together,” Drevon said. “They are not looking for a fight with [the SDF] . . . they aren’t going to antagonise a US ally.”
Another variable will be how Donald Trump approaches Syria and the deployment of US soldiers in the country after he takes office in January.
In his first term, Trump threatened to pull US troops out of Syria, triggering a backlash at home and abroad, and then appeared to greenlight a Turkish offensive against the SDF. He repeated this month that the US “should have nothing to do” with Syria.
But Daniel Byman, a director at the Center for Strategic and International Studies, said Trump’s unpredictability makes anticipating his next steps difficult.
“The president has been all over the map on this issue,” he said. “He’s been seemingly supportive of a greater Turkish role, but having said that he had four years previously to pull the US out of Syria and he didn’t.”
Additional reporting by Felicia Schwartz in Washington
Cartography by Steven Bernard and data visualisation by Aditi Bhandari