The Islamic State’s attacks in Paris and Belgium have demonstrated key vulnerabilities in European law enforcement and intelligence agencies. For several years, members of the Europe-based Islamic State network responsible for the attacks had moved through Turkey to join with the group in Syria. From the outset of the Syrian conflict, Turkish–European cooperation on this issue has been poor, with European authorities withholding information about potential fighters over privacy concerns, and Turkish authorities making little effort to prevent cross-border transit to and from Syria until late 2014 — the same time as the passage of United Nations Security Council Resolution 2178, which addressed the foreign fighter issue.

To date, much of the attention in the West and Turkey has been on the threat from European fighters, travelling from Europe, through Turkey, and into to Syria — and vice versa. However, Turkey faces risks from Turkish Islamic State fighters, many of whom have spent time in Syria, and have been able to return to cities in Turkey. Islamic State fighters and sympathizers have carried out seven attacks in Turkey since January 2015. The perpetrators of five of these attacks are all linked to one, active Turkish Islamic State cell, previously based in the southeastern town of Adıyaman. This cell operated for close to a year in the city with little interference from the Turkish authorities, despite local residents complaining to police forces that the house was doubling as an ISIL recruitment center. The group’s reported leader, Ilham Balı, reportedly fled to Syria in March 2015 before the start of an internal crackdown on Islamic State networks began inside Turkey.

The other two attackers were foreigners. The first was an 18-year-old pregnant woman from Dagestan, whose husband was reportedly an Islamic State fighter killed during the battle for the Kurdish town of Kobane. The Dagestani woman, Diana Ramazanova, killed one police officer, detonating a crudely constructed suicide bomb outside a police station in Sultanahmet — Istanbul’s most important tourist destination. The second attacker, Nabil Fadli, a 28-year-old Saudi national living in Syria, detonated a suicide vest in the ancient Byzantine Hippodrome next to Istanbul’s iconic Blue Mosque, killing 11 tourists.

ISIL has deep roots in Turkish society and links to other jihadi hotpots around the globe. Turkish ISIL members, or Turks with close links to the group, have taken advantage of legal loopholes in Turkey to avoid lengthy prison sentences or arrest altogether. These loopholes remain in place. Taken together, these dynamics create a potent ISIL threat to Turkey in the immediate future. Yet, despite this risk, little is known about the root causes of radicalization in Turkey, other than that the ISIL members involved in the current wave of violence were radicalized outside of mainstream mosques in Turkey, and instead were receiving religious training in unofficial gathering places, where radical proselytizing takes place. New recruits, in turn, were then able to move freely to the border, where they could cross to Syria with ease up until late 2014 and early 2015.

The Islamic State’s Network in Turkey

The Islamic State has well-established networks in Turkey, with clusters of people based in Istanbul, Ankara, Konya, Adana, Izmir, ŞanlıUrfa and the Gaziantep. These networks funnel men and material to the Syrian civil war, with the city of Gaziantep serving as a key hub for cross-border trade and the manufacture of suicide vests and explosives used in at least two Islamic State attacks in Turkey. The Islamic State used to rely heavily on the Akçakale border gate, opposite the Syrian city of Tel Abyad, before the Kurdish Democratic Union Party took control of the town in June 2015. The two nodes in Gaziantep and Şanlıurfa, in turn, are linked to known ISIL hotspots throughout the country and branch out to places as far west as Istanbul and east to Diyarbakır.

The Islamic State appears to have grafted on to older, well-established Al Qaeda-linked networks in Turkey. In at least two instances (Osman Karahan in Istanbul and the Konya-based Mustafa Guneş), Turkish men helped to recruit for Al Qaeda affiliates. In both cases, these men also had links to veterans of the Afghan jihad in the 1980s. In a third instance, an Adana-based Islamic State recruiter, known only as “Eyup Hoca,” also has links to Afghanistan — although it is unclear if he is tied to the 1980s fight against the Soviet Union or the current Taliban-led insurgency against the United States.

Mustafa Guneş is linked to Metin Kaplan, a radical Salafi previously based in Germany’s Cologne, who met with Osama Bin Laden in 1997, and is now imprisoned in Turkey after his extradition from Germany in 2005. Guneş has a long history of support for Al Qaeda. He is accused of plotting to attack Jewish and Western targets, before Turkish police raided a network of safe houses near Istanbul linked to him in 2008. Guneş reportedly fled to Egypt, but did at some point return to Turkey, where he hosted religious courses at a book store he owned in Konya, historically Turkey’s most Islamist-inclined city. This shop doubled as an ISIL recruitment center, according to leaked testimony from an unnamed female suicide bomber who attended these courses. Guneş’ recruiting methodology is nearly identical to that of the Adıyaman cell, where recruiters Ahmet Korkmaz and Mustafa Dokumacı both lectured about ISIL and religion to potential recruits before the start of Adıyaman-linked attacks in Turkey. A similar network was active in Izmir, under the direction of a man known as Sarı Murat (This is a code name. His initials are M.G.), the leader of the cell that radicalized Savaş Yıldız, the man responsible for two ISIL-linked attacks in Turkey in May 2015.

The prevalence of Al Qaeda-linked individuals in Turkey before the outbreak of the Syrian civil conflict in 2011, and the subsequent establishment of Jabhat al Nusra and the entry of the Islamic State into Syria from Iraq, underscore the complexity of the challenge Turkey — and Europe — now face. The Islamic State is taking advantage of previous conflicts to hone operational skill and develop new techniques to evade capture and detection by law enforcement. It also suggests that the networks Turkish and foreign fighters rely upon are deeply embedded in Turkey, with iterations dating back to the Afghan jihad during the 1980s, in addition to more modern conflicts like Iraq (2003–present) and Syria (2011–present).

Islamic State in Turkey: Operations

For many Turkish ISIL members, two interrelated events contributed to the decision to attack targets in Turkey: the Islamic State’s failure to capture the Kurdish held town of Kobane and the subsequent U.S.-backed Kurdish offensive to take Tel Abyad. This Syria-based offensive has reverberated inside Turkey, resulting in increased tensions between the religiously conservative and the avowedly secular, and PYD sympathetic, sub-sets of Turkey’s Kurdish population (Even many observers of Turkey are not aware that, despite the prominence of the secular PKK, Kurds as a group are one of the most religiously conservative segments of Turkish society).

The PYD-led battle for Kobane has galvanized feelings of cross-border pan-Kurdish nationalist sentiment in Turkey. It has also elicited a reaction from Islamists, hostile to the PYD. In October 2014, the co-chair of the leftist Kurdish-majority Democratic Peoples’ Party (HDP) called for the party’s supporters to protest Turkey’s approach to the Kobane conflict, wherein the Turkish military surged forces to the border, but did not intervene on behalf of the PYD, or allow Kurds from Turkey to fight to defend the city.

The HDP protest turned into riots and resulted in more than 30 deaths, the majority of which were members of Huda Par, a Salafi political party linked to Kurdish Hezbollah — a militia that fought the Kurdistan Workers’ Party (PKK) in Turkey’s southeast during the 1990s. These clashes helped to radicalize at least one Islamic State member in Turkey, Orhan Gönder, who on the eve Turkey’s June election detonated two crude explosives at an HDP political rally in Diyarbakır. The blast killed four.

Gönder travelled to Syria in 2014 with two brothers, Şeyh Abdurrahman and Yunus Emre Alagöz. Şeyh was the Suruç bomber, while Yunus Emre was one of two suicide bombers that targeted a gathering at the Ankara train station. The second Ankara train station bomber has yet to be identified, but reports indicate he is not a Turkish national. In a recent raid in Gaziantep, Turkish police arrested six Syrian nationals tasked with conducting attacks in Turkey. At least one of the arrestees has reported links to the foreign-born Ankara bomber.

These recent arrests suggests that Turkish and Syrian ISIL members have operational linkages, further suggesting a more senior, Syria-based leader in charge of the group’s Turkey operations. The attacks’ targets thus far show a deep understanding about Turkish society, particularly cleavages between nationalist and Islamist Kurds, both of which have allied political interests from Turkish leftists and the religiously conservative right. The Islamic State attacks in Adana and Mersin, Diyarbakır, Suruç, and the Ankara train station all targeted symbols of the Turkey-based nationalist Kurdish political movement, reflecting the PYD–ISIL tensions inside Syria.

This increase in attacks prompted the Kurdistan Workers’ Party (PKK) to retaliate against the Turkish government, which the group believes supports ISIL — and was therefore complicit in these attacks. In March, the AKP “froze” peace talks with the PKK; subsequently in July, two men with links to the PKK killed Turkish police officers in Şanlıurfa, purportedly in retaliation for the ISIL Suruç attack. This uptick in violence in July helped to undermine a two-year-old PKK–Turkish government cease-fire, setting in motion a chain of events that has resulted in resumption of a PKK-led insurgency — and heavy-handed state security operations to suppress it — in Turkey’s Kurdish-majority southeast.

ISIL had a hand in fomenting these tensions, which suggests local knowledge from the planner(s) of the six attacks (Diana Ramazanova’s suicide attack, it seems, is the outlier). According to the New York Times’ Rukmini Callimachi, ISIL’s external operations branch recruits foreigners for attacks in third countries, granting these operatives considerable autonomy once they are sent back to carry out attacks. ISIL refined these tactics with French and Belgian fighters over a period of time, before the cell responsible for the recent wave of attacks in both countries proved succesful.

ISIL uses similar tactics for operations in Turkey, creating Turkish-speaking units, complete with Turkish imams and military instructors. There is no open-source reporting that gives a clear indication about operational training, but there are indications that Turkish ISIL members take precautions to avoid electronic detection. Two days before carrying out the Diyarbakır attack, for example, Orhan Gönder was given three prepaid Turkish cell phones and instructions about how to travel from Gaziantep to Diyarbakir without being detected — tactics ISIL also used in Europe. Gönder was arrested before carrying out the June 7 election attack, but for dodging military service rather than for suspected ties to ISIL. He was let go and arrested again in Gaziantep, albeit after carrying out the attack, and presumably while trying to make his way back to Syria. His intial arrest and release does also suggest that Turkish authorities don’t have access to a comprehensive data picture about potential ISIL members, a problem that French and Belgian security services also have to varying different degrees.

ISIL’s attacks in Turkey, however, do have key differences from the recent Belgium attacks. The Belgian and French attackers mixed their own explosive, triacetone triperoxide (TATP), whereas the Turkish bombers relied on suicide vests made of a mix of TNT and Composition B, a castable mixture of TNT and RDX. This difference in explosives is, in all likelihood, due to the difficulty a Europe-bound ISIL member would have smuggling such a device on a flight to Europe. However, in at least two of the attacks (Suruç and Ankara), the suicide vests were manufactured at a Gaziantep warehouse, rather than in Syria. It is unclear, however, where the explosives were procured. This suggests a robust ISIL presence inside Turkey, perhaps built around the smuggling networks that the group relies upon to help sustain its self-declared caliphate. The recent arrests of Syrians with links to the Adıyaman cell suggest that this link remains in place, despite a surge in ISIL-related arrests in Turkey since March 2015 and concurrent efforts to close the border.

Building a Profile: A Difficult Challenge

The Adıyaman cell’s involvement in Islamic State activities is straightforward: The group is responsible for five attacks and the failed attack on New Year’s Eve. This group operated overtly for close to a year in Adıyaman, before key members fled for Syria. A large number of this group’s members spent time in Syria in 2013 and 2014. In at least one instance, a Turkish ISIL member was working in a refugee camp near the border, before he was recruited to attend religion courses Ahmet Korkmaz, the spiritual leader of the Adıyaman cell, taught at his home. This experience with the war in Syria, obviously, contributed to the radicalization process. ISIL members all also attended religion courses, taught by extremists. In Adıyaman, Korkmaz acted as both a spiritual guide and a recruiter. In Konya, Mustafa Guneş reportedly operated in much the same way.

Like Guneş and Kormaz, Sarı Murat ran an informal religious community (cemaat), where he recruited for ISIL. After four months of religious training, Murat sent his recruits to Syria to join ISIL, where they received more religious and military training in Tabka, Syria, just outside of Raqqa. Murat’s cemaat was well known to elements of Turkey’s Salafi community. Turkish police arrested Murat and known associates recently, after the YPG posted Yıldız’s interrogation video online. The commonalities in recruitment efforts across multiple different Turkish cities suggests that authorities must act more quickly to detain recruiters and spiritual emirs, or otherwise risk larger numbers of people being exposed to ISIL ideology.

However, there does not seem to be a generic profile of recruiters or fighters, making the aforementioned process more difficult. Turkish ISIL members are Kurdish, Sunni, Bektaşi Alevi, and come from both highly and poorly educated families. One member was a PhD candidate studying to become an astrophysicist. Another is a drug addict, now parking cars in Ankara after spending two different stints with ISIL in Syria to help kick his habit. The group’s fighters do appear to be younger than Turkish supporters of Al Qaeda, but that is also not a hard rule: Adnan Yıldırım, the captured ISIL-linked New Year’s Eve bomber is 40, whereas his accomplice, Musa Canöz, is 28.

This suggests that ISIL’s appeal is cross-generational, cross-confessional, and also not confined to one area inside Turkey. However, key ISIL recruiters, fighters who joined with either ISIL or Nusra, and at least one Turkish ISIL suicide bomber do share links to the Afghan jihad. Taken together, this key data point suggests that the backbone of the Turkish ISIL networks pre-date the current conflict in Syria. The data suggests that the current conflict has expanded the ranks of potential recruits. Şeyh Abdurrahman Alagöz was 20 when he detonated his suicide vest, whereas the group’s leader, Mustafa Dokumacı, was born in 1985. At the start of the Syrian conflict, Alagöz was only 15. Dokumacı was 26. Walentina Slobodjanjuk, a German national originally from Kazakhstan who married one of the Turkish ISIL members in a religious ceremony in Syria, was born in 1995 — making her just 16 when the conflict began.

This demographic may be more susceptible to ISIL propaganda, benefitted from the ease with which one could travel to and from Syria via Turkey between 2011 and 2015, and gravitated towards radical elements inside Turkey. Turkey and Europe face a common problem: The longer-term implications of radicalized citizens that have fought in Syria or support ISIL’s religious ambitions.

On April 1, Turkish media reported that authorities are looking for five potential suicide bombers: Abu Ayman at-Maghribi (A Moroccan-American), Rashed Alabdalah Algaagan (who has a reported link to Nabil Fadli, the Sultanahmet bomber), Isa Tupolov (An Azeri with a Russian passport), and Furkan Ürkmez and Hasan Hüseyin Uğur (both Turkish citizens). Furkan’s brother, Muhamed Ürkmez, was killed fighting with ISIL in July 2015. The Turks appear to be Syria-based, while the other foreigners have reportedly entered Turkey. This collection of individuals, with two Syria-based Turks, lends more credibility to the notion that there is a common, Syria based ISIL network directing attacks in Turkey. This network, it seems, is multinational, but it is relying on Turks for strategy. However, this cannot be confirmed — and remains a hypothesis that must be proved.

The Turkish case does not point to an identifiable pattern of radicalization; instead, ISIL members come from diverse backgrounds. Turkish ISIL members appear to have links to a number of foreigners, many of whom appear to have travelled through Turkey at some point before 2015. This Syria-based network has grafted on to older, established Al Qaeda groupings, linked to other global jihadi hot spots. This problem is not unique to Turkey, but the crackdown against these networks only appears to have started in late 2014 and early 2015. Thus, in the longer term, both Europe and Turkey must together face a shared set of ISIL-linked challenges, both with intelligence cooperation, but also with domestic legislation. Turkey has an incentive to tackle the latter issue first while also continuing its efforts to prevent foreign fighters from using its territory to transit to Syria. However, once ISIL is defeated, the issue of radicalization will remain a threat to Turkey, with no easy policy solution to address the problem.

Aaron Stein is a Resident Senior Fellow at the Atlantic Council’s Rafik Hariri Center for the Middle East.