Deprivation of Liberty

Customary IHL prohibits arbitrary deprivation of liberty.¹ The arbitrary nature of such deprivation comes from either the lack of legal grounds for detention of a person or the unlawful procedure by which a person is detained. Any detainee must be able to challenge the legality of their detention (habeas corpus).

Detention in connection with criminal proceedings

In international armed conflict, individuals (whether prisoners of war or other detainees, including civilians) may be detained in relation to the prosecution that should follow the commission of war crimes.² 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 In all armed conflict, 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

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. IHL rules governing internment differ depending on whether the situation is classified as an international or non-international armed conflict. In NIAC, 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 international armed conflicts, which sets out 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 ended.

Internment in IACs

In international armed conflicts, the applicable rules depend on the status of the individual. Combatants who fall in the power of the enemy are prisoners of war (PoWs) who can be detained until the cessation of active hostilities.⁵ 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 on an individual basis, following the decision of a board on the grounds of internment. There must be the possibility of appeal and a review of the decision every six months.⁶ PoWs must be held in camps that meet specific standards.⁷ In any case, imprisonment in confined spaces without daylight is prohibited.⁸ Only in extreme circumstances may the communication rights of civilians be restricted.⁹

Internment in NIACs

In non-international armed conflict, IHL 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.¹⁰ Domestic law, which is governed by a State’s human rights obligations and IHL, regulates the right of internment by State authorities.¹¹ Customary IHL requires grounds and procedure for internment, and if there are not — or no longer — any valid reasons for deprivation of liberty it becomes arbitrary and thus unlawful.¹² The detaining authority is responsible for ensuring that the conditions of internment of detainees are fulfilled, including their rights to communicate with the outside world.¹³

Treatment

IHL demands that all persons deprived of liberty be treated humanely and with dignity, and prohibits torture and any form of ill-treatment, regardless of the conflict classification.¹⁴ The taking of hostages (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.¹⁵

IHL entrusts the International Committee of the Red Cross (ICRC) with the right, in international armed conflict, to regularly visit and privately interview with PoWs and civilians deprived of liberty, wherever they are. The detaining State may not prevent these visits except for imperative and temporary security reasons.¹⁶ In NIACs, ICRC visits require the approval of the territorial State, which is not legally obliged under IHL to grant access.¹⁷

1
ICRC, Customary IHL Study Rule 99: ‘Deprivation of Liberty’, https://ihl-databases.icrc.org/en/customary-ihl/v1/rule99
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
3
Art 64 GC IV
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
5
Arts 21 and 118 GC III
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’)
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
8
Art 87(3) GC III; Art 118(2) GC IV
9
Art 5 GC IV.
10
See Common Art 3 GCs; Art 4(1) and 5 AP II
11
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
12
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
13
Art 5(2)(b) AP II
14
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
15
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
16
Art 126 GC III; Art 143 GC IV.
17
Common Art 3 GCs