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War Watch
Legal Explainers

Deprivation of Liberty

IHL prohibits arbitrary deprivation of liberty.1 ICRC, Customary IHL Study Rule 99: ‘Deprivation of Liberty’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule99 The arbitrary nature of such deprivation, and therefore its unlawful character, flow from either the grounds or the procedure. On the other hand, IHL envisages different situations during armed conflict where belligerents may detain individuals on the basis of lawful grounds. Finally, IHL also governs the conditions of deprivation of liberty and the treatment of the persons deprived of liberty.

Detention in connection with criminal proceedings

In several situations, detention during armed conflict takes place in connection with criminal proceedings related to the conflict. Individuals (both prisoners of war and civilians) may be detained in relation to the prosecution that should follow the commission of war crimes.2 Art 49 GC I; 50 GC II; Art 129 GC III; Art 146 GC IV; Art 85(1) AP I; ICRC, Customary IHL Study, 158: ‘Prosecution of War Crimes’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule158 In situations of belligerent occupation, civilians in occupied territory may be detained for having committed offences in breach either of local penal laws, or of penal provisions promulgated by the Occupying Power under certain conditions.3 Art 64 GC IV Finally, both in IACs and in NIACs civilians who participate in hostilities may be prosecuted domestically, to the extent that taking up arms and causing harm in doing so are criminalized under national law.4 N. Melzer, ‘Interpretive Guidance on the Notion of Direct Participation in Hostilities under International Humanitarian Law’, ICRC, May 2009, Section X.1, p 84. On the other hand, whether armed groups can prosecute and detain those who are fighting against them is still an open question  

Internment

A particular form of detention that may, under strict conditions, take place in the context of armed conflict is internment – i.e., detention for security reasons related to the armed conflict. The IHL rules governing internment largely differ according to whether the situation is classified as an IAC or a NIAC. In the latter, IHL only provides basic rules on the treatment of persons deprived of liberty, offering no explicit provisions regarding the grounds for internment or the procedure to be followed. In contrast, a comprehensive and detailed regulation exists for IACs, which sets forth the grounds for detention and internment of combatants and civilians in occupied and own territory, as well as their treatment and release once the grounds for internment have ceased.

Internment in IACs

In IACs, there are different regimes applicable depending on the status of the individual. Regarding the grounds of deprivation of liberty, combatants who fall in the power of the adversary and obtain the status of prisoners of war (PoWs) can be interned until the cessation of active hostilities, on the sole basis of their status, without the need for any particular procedure.5 Arts 21 and 118 GC III In contrast, the internment of civilians whose activity is deemed to pose a serious threat to the security of the detaining State must be done (whether in occupied or in own territory) on an individual basis, following the decision of a board on the grounds of internment, with the possibility of appeal, and subject to the review of the decision every six months.6 See Arts 42 and 43 GC IV for the provisions applicable in a State party’s own territory (which refer to internment and assigned residence when ‘the security of the Detaining Power makes it absolutely necessary’), and Art 78 GC IV in the context of occupation (internment and assigned residence ‘for imperative reasons of security’) While different conventions regulate the treatment of interned PoWs and civilians, the basic guarantees and conditions of internment remain largely comparable, differing only in a few respects. Notably, PoWs must be held in camps that meet specific standards and cannot be interned in penitentiaries, as may sometimes be the case for civilians.7 The conditions of internment, rights and guarantees of interned PoWs are regulated in Part III (Arts 21–108) of GC III. For places of internment, see Arts 22 and 97 GC III Nevertheless, imprisonment in confined spaces without daylight is explicitly prohibited in both cases,8 Art 87(3) GC III; Art 118(2) GC IV and confinement is permitted solely as a disciplinary measure, subject to particular safeguards.9 Art 98 GC III; Art 125 GC IV In any case, PoWs and civilian internees, including those awarded disciplinary punishment, are entitled to write and receive correspondence and, in the case of civilians, to also receive visits.10 For correspondence, see Arts 71, 98(5) and 108(3) GC III; Arts 25, 107 and 125 GC IV. For visits, see Art 116 GC IV Only in extreme circumstances may the communication rights of civilians be restricted.11 Art 5 GC IV.

Internment in NIACs

In NIACs, IHL only offers basic guarantees for the treatment of persons deprived of liberty in relation to the conflict, without explicitly regulating the grounds or the procedure for internment of enemy fighters or civilians who pose a serious threat to the security of the detaining authority.12 See Common Art 3 GCs; Art 4(1) and 5 AP II The lack of a regulatory framework has sparked significant debate over the legal basis and features of internment in NIACs, despite AP II explicitly mentioning internment and therefore qualifying it as inherent also to this type of armed conflict.13 Art 5(2) AP II; ICRC, ‘Internment in Armed Conflict: Basic Rules and Challenges – Opinion Paper’, November 2014, https://www.icrc.org/sites/default/files/document/file_list/security-detention-position-paper-icrc-11-2014_0.pdf; ICRC, Updated Commentary on GC IV, 2025, paras 754–765; T. Rodenhauser, ‘Internment by non-state armed groups: legal and practical limits’, Humanitarian Law and Policy Blog, 15 October 2024, https://blogs.icrc.org/law-and-policy/2024/10/15/internment-by-non-state-armed-groups-legal-and-practical-limits/ Domestic law, informed by a State’s human rights obligations and IHL, has been advanced as the appropriate legal framework for internment carried out by State authorities in a traditional NIAC pitting government armed forces against one or more organized armed groups.14 ICRC, ‘Internment in Armed Conflict: Basic Rules and Challenges – Opinion Paper’, November 2014, p 7, https://www.icrc.org/sites/default/files/document/file_list/security-detention-position-paper-icrc-11-2014_0.pdf; ICRC, Updated Commentary on GC IV, 2025, para 763 On the other hand, the identification of the legal framework governing internment by non-State armed groups continues to present considerable challenges, and has so far been addressed chiefly by means of institutional guidelines.15 See J. Pejic, ‘Procedural principles and safeguards for internment/administrative detention in armed conflict and other situations of violence’, 87 IRRC (2005), pp 375–392 Despite uncertainties as to their precise contours, customary IHL undoubtedly demands that some grounds and procedure for internment be provided by the detaining authority, and that valid reasons for such deprivation continue to exist, lest the detention becomes an arbitrary one.16 ICRC, Commentary to Customary IHL Rule 99: ‘Deprivation of Liberty’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule99; ICRC, Updated Commentary on GC IV, 2025, para 756 Moreover, the detaining authority remains responsible for ensuring that the conditions of internment of the persons deprived of liberty are fulfilled, including their rights to communicate with the outside world.17 Art 5(2)(b) AP II

          Treatment

Despite these differences, IHL consistently mandates that all persons deprived of liberty be treated humanely and with dignity, without any adverse distinction, and prohibits torture and any form of ill-treatment, regardless of the conflict classification.18 Common Art 3 GCs; Arts 13 and 14 GC III; Arts 27 and 32 GC IV; Art 75 AP I; Arts 4 and 5 AP II Under all circumstances, the taking of hostages (i.e., deprivation of liberty of an individual followed by threats against them to compel a third party to do or to abstain from doing any act) is strictly forbidden in IHL in all armed conflicts.19 Common Art 3 GCs; Art 34 GC IV; Art 75(2)(c) AP I; Art 4(2)(c) AP II; ICRC, Customary IHL Rule 96: ‘Hostage-Taking’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule96 

To ensure the respect for the law, safeguard the proper treatment of persons deprived of liberty, as well as restore contacts between those persons and their families, IHL has entrusted the International Committee of the Red Cross (ICRC) with the right, in IACs, to regularly visit and privately interview with PoWs and civilians deprived of liberty, wherever they are, which the detaining State cannot oppose except for imperative and temporary security reasons.20 Art 126 GC III; Art 143 GC IV. Conversely, in NIACs, ICRC visits require the approval of the territorial State, which is not legally obliged under IHL to grant access.21 Common Art 3 GCs