Since the fall of its self-proclaimed caliphate in 2019, ISIS remains a persistent threat in Syria. As of 2025, according to US estimates, more than 2,500 active fighters continue to operate in Syria and Iraq, while thousands of battle-hardened ISIS militants are held in Syrian prisons – posing a serious risk if released, especially through orchestrated prison breaks. Additionally, thousands of ISIS-affiliated individuals remain in detention camps, where they are vulnerable to radicalization and recruitment. Following the fall of the Bashar Al-Assad Ba’ath regime, the tenuous control of the new Syrian government, combined with ongoing violence, could further strengthen ISIS’s capabilities, allowing jihadists to regroup, sustain their presence, and potentially expand their influence once again.
Beyond Syria and Iraq, ISIS has significantly expanded its presence and influence across several countries in Africa and Asia. However, due to the dynamic developments following the fall of the Al-Assad regime and the ongoing political transition in Syria, this article will focus exclusively on ISIS in Syria, one of its core strongholds alongside Iraq. This analysis will assess the group’s current state, operational strengths, and the persistent terror threat it poses to Syria.
The Rise and Fall of the ISIS-Caliphate: A Background Overview
The Sunni jihadist group ISIS is known by various names, including IS (Islamic State), or Da’esh – its most common name in the Arab world – an acronym for its Arabic name, Al-Dawla Al-Islamiya fi Al-Iraq wa Al-Sham, which translates to the Islamic State of Iraq and the Levant (ISIL). ISIS traces its origins to Al-Qaeda in Iraq (AQI), which emerged in the aftermath of the 2003 U.S. invasion in Iraq that toppled Saddam Hussein’s Ba’ath regime. Under former leader Abu Bakr Al-Baghdadi, ISIS expanded rapidly, exploiting instability in Iraq and Syria’s civil war. By the summer of 2014, it had overrun both Iraqi and Syrian government forces, seizing nearly one-third of both countries – an area roughly the size of England. On June 29, 2014, the group declared a global caliphate, with Al-Baghdadi proclaiming himself caliph, or leader, of the worldwide Muslim community. In the years that followed, ISIS became the world’s most notorious terrorist organization, enforcing a rigid interpretation of Islamic Shari’a law, committing mass killings, and displacing millions. Notably, in August, it committed genocide against the Yazidi minority in Iraq, executing thousands of men and enslaving women and children, subjecting them to systematic sexual violence.
Moving beyond the typical development of a terror organization, ISIS established broad proto-state structures and forms of governance, ruling through fear and brutality. At its peak, it governed around 12 million people and built military structures, employing a hybrid of guerrilla and conventional tactics. The group was estimated to have more than 50,000 fighters from over 100 nations. However, by December 2017, the U.S.-led Global Coalition Against Daesh had recaptured 95% of the territory ISIS had occupied. The group’s final stronghold, Baghouz, fell to the U.S.-backed Syrian Democratic Forces (SDF) in 2019, marking the collapse of the self-styled caliphate.
The Shadow of ISIS in Syria: A Persistent Danger
Today, however, the threat posed by ISIS militants in Syria is more severe than in any other country in the region, including Iraq. This is primarily due to recent sectarian violence, ongoing hostilities in various parts of the country, the threat of a limited-scale insurgency by remnants of the former Al-Assad regime, and, most critically, the presence of thousands of ISIS jihadists – both active fighters and detainees – who could fuel a resurgence. But what exactly makes ISIS a persistent danger in Syria, and how does this threat challenge the country’s post-Al-Assad landscape?
In 2019, the U.S. President Donald Trump announced a “100 percent victory” over ISIS, yet the reality tells a different story. While thousands of ISIS fighters were killed, and thousands were detained during the liberation campaigns in Iraq and Syria, an estimated 2,500 battle-hardened militants remain active. Though massively weakened, they remain agile, primarily in Syria, where many operate in clandestine sleeper cells. UN estimates from 2021 suggested that up to 10,000 militants remained active in Iraq and Syria. The continued presence of jihadists with extensive combat experience and the capability to conduct targeted attacks poses a serious threat. Despite years of intense military pressure from the international coalition to dismantle its operations and prevent its resurgence, ISIS has demonstrated remarkable adaptability and is actively rebuilding itself. The sustained counterterrorism efforts and targeted killings of high ranking ISIS figures by the Global Coalition to Defeat Daesh, such as the recent elimination of Abu Khadijah – reportedly the second-in-command of ISIS worldwide – reflect the group’s enduring threat.
Following the loss of its territory and its shift back into an underground insurgency, ISIS has been operating mainly in two key regions: the Syrian Desert (Badiya Al-Sham), which covers more than half of the country, and the Jazira Region (Northeastern Syria), largely controlled by Kurdish forces. Taking advantage of these remote, poorly governed, and difficult-to-access areas, the group continues to regroup, train new recruits, and launch terror attacks, using the vast desert terrain as a safe haven for sustained insurgent activities. The sharp escalation in ISIS attacks over recent years illustrates the persistent and growing threat posed by jihadists in Syria. Since its territorial defeat, ISIS has continually launched attacks across Syria, primarily targeting Assad’s forces, their Shi’a allies, and Kurdish armed groups. Reports indicate that in 2023 alone, ISIS was responsible for over 200 attacks, resulting in hundreds of casualties, including more than 285 soldiers and more than 231 civilian deaths. By 2024, this number had more than tripled, with ISIS carrying out around 700 attacks, causing over 750 deaths, including both military personnel and civilians.
ISIS has transformed from a territorial regime to a mobile and decentralized insurgent force, possessing a vast arsenal of weapons. Their resources also include caches of cash and gold hidden in the desert during its territorial decline to ensure the future continuation of their terrorist activities. Moreover, some indications suggest that large amount of weaponry from the Al-Assad’s army, as well as potentially from the Russian military, fell into ISIS’s hands following the fall of the Al-Assad regime in December 2024. These weapons would bolster their firepower and resources and enabling them to intensify their insurgent operations. The regime’s collapse was brought about by Hayat Tahrir Al-Sham (HTS)-led Sunni Islamist rebel groups under the command of Ahmed Al-Shara’, a former Al-Qaeda affiliate. HTS designated a terrorist organization, which later declared its dissolution on January 29, 2025, integrating its forces and organizational structures into the new Syrian state institutions.
Another key factor sustaining the ISIS threat in Syria is the fragile political environment following Al-Assad’s downfall, exacerbated by competition and occasional armed conflicts between rival factions with different political and ethno-religious backgrounds, alongside the influence of external actors in the country. A notable example is that the Kurdish forces, particularly through the SDF, continue to fight for autonomy and control in the northeast of the country – Rojava, a de facto autonomous region lead primarily by Kurdish leadership – while facing constant pressure from Turkey and its Islamist allies, such as the Syrian National Army (SNA). Despite a landmark agreement signed on March 10, 2025, between the Kurdish Commander-in-Chief of SDF Mazloum Abdi and interim President Ahmed Al-Shara’, which foresees the integration of SDF-controlled institutions and forces into Syrian state institutions in exchange for “constitutional rights”, including linguistic rights, the extent of this integration remains uncertain. The debate over Syria’s governance – centralized versus decentralized? – remains a contested issue. Kurdish leadership continues to advocate strongly for decentralization and is unlikely to abandon their ambitions for Rojava’s autonomy. Meanwhile, the unstable interim government struggles to assert its authority nationwide. Sectarian and ethnic divisions, intensified by decades of brutal dictatorship and the brutal civil war, have left lasting grievances. Between March 6 and March 12, 2025, security forces and affiliated elements of the new government, which includes a strong Sunni Islamist presence, massacred an estimated 800 to 1,500 civilians, including women, children, and the elderly in coastal areas. Although the exact number varies across different reports, mostly from the Alawite minority – a Shiite offshoot to which Al-Assad’s clan belongs and which represented the power base of the deposed regime – further intensifying sectarian tensions. This sectarian violence erupted after remnants of the deposed regime launched assaults on the new Syrian forces.
These divisions and the government’s lack of control over the whole country create fertile ground for ISIS to exploit governance voids and public unrest, positioning itself as an alternative form of governance and expanding its influence. Moreover, the interim administration faces significant challenges, particularly in remote areas, due to a lack of security personnel, allowing ISIS to regroup and operate with relative ease.
Another crucial aspect of the ISIS menace in Syria is the imprisonment of over 10,000 ISIS fighters in an SDF-controlled network of 28 detention facilities, along with nearly than 60,000 of their family members held in northeastern Syria. These facilities are “ticking time bombs”, as ongoing hostilities between Kurdish forces and Islamist factions further destabilize the region, weaken security measures, and raise the risk of large-scale prison breaks. This vulnerability was demonstrated in January 2022, when ISIS launched a coordinated attack on Al-Sina’aprison in Al-Hasakah, following the strategy of “Breaking the Walls“ – a year-long ISIS campaign in Iraq starting in July 2012, during which they freed hundreds of jihadists, significantly contributing to their resurgence at the time. The attack on Al-Sina’a allowed hundreds of jihadists to escape. ISIS remains determined to free its imprisoned members, as they represent a crucial part of its future fighting force, a threat reflected in the words of CENTCOM spokesperson Colonel Joe Buccino, who called them “ISIS army in detention”. Since the regime’s collapse, Kurdish forces report that ISIS has attempted two attacks on prisons. Additionally, camps like Al-Hol and Roj have become radicalization hubs, especially for young boys, who are another essential “human reservoir”, groomed for ISIS’s “Cubs of the Caliphate” program. These camps face significant violence, including assassinations, as ISIS loyalists maintain control in areas, despite Kurdish oversight, which is hindered by limited resources – an issue that could potentially worsen following the recent aid cuts by the Trump administration. In the event of mass prison breaks or the release of both detained ISIS fighters and their radicalized family members, the consequences would be catastrophic, reinforcing ISIS’s ranks, restoring its operational capabilities, and destabilizing not only Syria’s fragile new governance but the entire region.
In summary, despite losing its territory in 2019 and facing ongoing counterterrorism efforts, ISIS remains an ongoing menace in Syria. The security vacuum and political instability following Al-Assad’s fall have left the country deeply divided, creating a fertile ground for ISIS to expand. With experienced fighters still active and the risk of prison breaks, ISIS continues to seek a resurgence, challenging Syria’s interim government and regional security.
Outlook
Although no large-scale fighting between the numerous groups active in the country erupted after the fall of the Assad regime, the situation in Syria remains difficult, marked by a volatile security landscape and instability, making the country’s future uncertain. One likely scenario is that ISIS may continue its habit of thriving in power vacuums, exploiting Syria’s divisions, intensifying asymmetric warfare against the interim government and Kurdish forces, and organizing mass prison breaks. This risk increases if instability persists, hostilities do not cease, the economic situation does not improve, and governance remains weak. Moreover, despite HTS’s rivalries with ISIS and distancing from Al-Qaeda, the group was once linked to both, and still harbors extremists with sympathies for ISIS’s ideology. Indeed, many HTS members even fought for ISIS at some point in the past. This raises concerns about the risk of renewed extremist violence. Since 2016/17, HTS has fought ISIS cells in Idlib when in control of the province. However, they likely cannot replicate this effort over the whole Syrian territory. Given the new government’s likely inability to fully control these factions, there is a real danger of ISIS alignment or resurgence, further aggravating Syria’s fragile situation.
In addition to addressing other potential challenges, a further significant challenge for the transition government will be dealing with the remnants of the deposed Al-Assad regime. Although no longer in power, these individuals, with their professional experience and established networks, still possess weapons and maintain some level of support, particularly in the coastal region, and could potentially anew attack the new Syrian forces, further destabilizing the country. It is crucial that those responsible for crimes under the Al-Assad regime are held accountable through justice, while preventing collective punishment, as such actions would obstruct efforts toward lasting peace. Furthermore, the perpetrators of a wave of mass killings against Alawite civilians – who were deliberately executed – must be held accountable. Ensuring justice for these brutal crimes is vital for national reconciliation and for fostering trust in the transitional government.
Amid Syria’s critical transition, external military shifts – such as a potential U.S. troop withdrawal, as proposed by Donald Trump – could further escalate the threat. The removal of approximately 2,000 U.S. troops, who particularly support SDF forces in countering ISIS, would ease pressure on the group, potentially enabling it to regroup and expand. This might mirror the situation in Iraq after the 2011 U.S. withdrawal, where weakened Iraqi forces significantly empowered ISIS to regain strength and capability. This step would weaken the SDF, endanger security, and heighten the risk of prison breaks.
In Syria’s transition, it is crucial to involve all ethnic and religious groups in governance while prioritizing reconciliation, the rule of law, and human rights. Addressing the shattered economy, rebuilding infrastructure, enabling the return of displaced people, and working to lift sanctions are essential for stability and for breaking the cycles of violence that fuel ISIS’s resurgence.
Masood Al Hakari
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