ISIS members detained by Kurdish forces in Syria: Operational and legal challenges

About the author(s):

Alessandra Spadaro is an Assistant Professor of Public International Law at Utrecht University. She obtained her PhD in international law from the Graduate Institute of International and Development Studies in 2021, with a thesis on detention by armed groups. She specializes in and has published on international humanitarian law, international human rights law, international criminal law, and their intersection.

ISIS members detained by Kurdish forces in Syria: operational and legal challenges

The Kurdish-led and US-backed Syrian Democratic Forces (SDF) are currently detaining over 3000 ISIS members, including foreign fighters and their families, in detention centers and camps in the North of Syria. Among them are British teenager Shamima Begum and her Dutch husband, Yago Riedijk, who have recently made headlines. Captured ISIS members in the hands of the Kurds come from over 46 countries, but – with some exceptions – most of these countries refuse to repatriate their citizens for various reasons despite numerous calls to do so by the SDF and the US. Some European countries are even stripping ISIS members of their citizenship in order to prevent their return.

While the responsibility of states supporting the detention operations of the SDF has been addressed elsewhere (see here and here), this post focuses on the practical and legal challenges for the detaining armed groups by analyzing four different options at their disposal: transfer, release, continued detention, and trial.


Transfer of the detainees is the option that the SDF would prefer. Recent reports indicate that some non-Iraqi ISIS members have been transferred to Iraq. The Iraqi Prime Minister has however announced that Iraq will only receive foreign fighters from the Kurdish forces in so far as they can be prosecuted by Iraqi tribunals for terrorist offenses committed in Iraq or can be transferred to their countries of origin. In addition to being problematic in practice, given the reluctance of the concerned states to receive the detainees, transfer is also not straightforward from a legal point of view. There is a real danger of violation of the fundamental rights of the detainees by some of the states to which they may be transferred. Such danger triggers the principle of non-refoulement. Although this principle is not explicitly mentioned in Common Article 3 (CA3), according to the 2016 ICRC Commentary, both states and non-state parties to non-international armed conflicts (NIACs) are prohibited from transferring persons in their power to another authority when they would be in danger of suffering a violation of fundamental rights upon transfer (paras. 708, 713). To comply with the principle of non-refoulement, the SDF should “assess carefully and in good faith whether there are substantial grounds for believing that the person would be subjected to torture, other forms of ill-treatment, arbitrary deprivation of life or persecution after transfer” and not transfer them until measures to remove this risk have been taken (para. 715). While the Commentary mentions post-transfer monitoring mechanisms that have been put in place by states and international organizations (para. 716), it does not elaborate on whether the same is expected of armed groups nor on whether armed groups would have the ability to do this. Although it seems unlikely to happen for the time being, the transfer of detainees to the Syrian government authorities, which have notoriously committed atrocities against detainees, might be hindered precisely by the principle of non-refoulement.

In light of the difficulties in transferring the detainees safely, the SDF may opt for a second choice: to release them. Reportedly, the SDF have already released hundreds of Syrians who only took up administrative jobs within the Islamic State. It is also reported to have discussed releasing fighters and their families. International law does not prohibit this second scenario and, indeed, release might be a valid solution to end an otherwise potentially unlawful detention. However, releasing thousands of ISIS members might have dire security consequences. Released fighters might go back to participating in the hostilities, and the progress made towards the territorial eradication of the Islamic State might be halted or even reversed. Some might also return to their countries of origin or travel elsewhere to carry out terrorist attacks in the name of ISIS and or to radicalize new recruits.

The third and, for now, most likely scenario is that the SDF might simply continue detaining the ISIS affiliates they have captured. Although the Kurds may want to redirect some of their resources against Turkish(-backed) forces once the US troops withdraw from Syria, at the moment they might continue investing them in the detention centers and camps. Given the stalemate on the transfer front, the US military has been funding the improvement of the capacity of the SDF to hold detainees and prevent jailbreaks. However, band-aids don’t fix bullet holes. In the long run, this situation is likely to become untenable: as the number of detainees keeps increasing, the already difficult conditions of detention in the Kurdish-run camps might further deteriorate. While Kurdish officials claim that conditions of detention especially for women and children and the treatment of detainees meet international standards, the Independent International Commission of Inquiry on the Syrian Arab Republic, among others, has reported otherwise (paras. 15-18, 44).

The hypothesis of continued detention is also problematic for other reasons, in particular the prohibition of arbitrary deprivation of liberty. Arbitrary deprivation of liberty is prohibited in armed conflict. In practice, in NIACs both states and non-state armed groups detain individuals whose activity is deemed to pose a security threat to them, but – as the readers of this blog probably know – the basis on which they may do so is subject to debate (see here and here for two different perspectives). According to the ICRC, IHL does provide an inherent power to detain but, in keeping with the principle of legality, grounds and procedure for deprivation of liberty in NIAC must be explicitly provided elsewhere (para. 728). It is uncertain whether such grounds and procedures have been adopted by the SDF, and whether they have created initial and periodical review mechanisms to ensure that each individual is given the chance to challenge the legality of their detention and is released once the reasons for detention have ceased to exist. In this context, indefinite and arbitrary detention is a real and frightening possibility.

It is also not clear whether all or some of the former ISIS affiliates are being detained for criminal or security reasons. Although they might be prosecuted in their home countries for membership in a terrorist organization or for war crimes, the detained women are not currently accused of any crimes and the Kurdish forces have had a hard time identifying their role within ISIS as well as determining “how much of the ideology they still endorse”. Additionally, by signing the Geneva Call Deed of Commitment for the Protection of Children from the Effects of Armed Conflict in 2014, the People’s Protection Units (YPG), which are the primary component of the SDF, undertook “to treat humanely children who are detained or imprisoned for reasons related to the armed conflict, in accordance with their age and gender specific needs, recognizing that deprivation of liberty may be used only as a measure of last resort and for the shortest appropriate period of time”.

On the other hand, based on infamous reports about the brutality of the Islamic State, at least some former fighters might be suspected of having committed international crimes, rather than being interned for security reasons alone. For reasons of brevity, the regulation of detention for the purposes of prosecution in NIAC will not be discussed in detail in this post. It is however worth mentioning that the fourth option for the SDF might in fact be to try at least some of the ISIS members they detain. Such trials might encounter more than one legal hurdle. Common Article 3 prohibits “the passing of sentences and the carrying out of executions without previous judgment pronounced by a regularly constituted court, affording all the judicial guarantees which are recognized as indispensable by civilized peoples”. The violation of this provision can be prosecuted as a war crime under Article 8(2)(c)(iv) of the Rome Statute of the International Criminal Court. While it seems possible for armed groups to establish courts meeting the requirements of Common Article 3, uncertainty regarding the applicable law (see here at para. 692) and the composition of such courts persists (see here at para. 33). Kurdish armed groups, like other groups with extensive control over territory, have established different types of courts in Syria to handle both civil and criminal cases (see here at pp. 106-107). Among them are ad hoc anti-terrorism courts, which however reportedly prosecute only Syrians and not foreigners. Additionally, the extent to which such courts are in fact able to grant a fair trial to defendants is questionable.

At the moment, none of the identified scenarios constitutes an acceptable solution. It is up to states to find one in agreement with the Kurdish forces. For instance, states might consent to have the detainees transferred to them or might decide to invest seriously in enhancing the capacity of the SDF to comply with international law rules relating to detention and fair trial. The hope is that the rights of detainees are given the paramount importance that they deserve, sooner rather than later.

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1 thought on “ISIS members detained by Kurdish forces in Syria: Operational and legal challenges”

  1. Pingback: Caught in the crossfire: responsibilities for ISIS members detained in North East Syria following Turkey’s Operation Peace Spring – Part I | Armed Groups and International Law

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