International humanitarian law 31. In addition to international human rights law, if an armed conflict exists, international humanitarian law applies. While international humanitarian law pertains to situations of armed conflict, international human rights law is applicable at all times and to all persons. Therefore, in situations that meet the threshold definition of non-international or international armed conflict, international human rights law and international humanitarian law apply concurrently and their various protections are complementary, not mutually exclusive. 32. Common Article 1 to the Geneva Conventions of 12 August 1949 provides that “[t]he High Contracting Parties undertake to respect and to ensure respect for the present Convention in all circumstances”, which has become part of customary international law and applies to international humanitarian law in general. Military necessity cannot be invoked as a justification for acts that are contrary to international humanitarian law,46 unless the rule in question specifically provides for exceptions based on military necessity. 33. Critical to some children affected by the foreign fighter phenomenon is the obligation to treat all children affected by armed conflict with special respect and protection under international humanitarian law.47 Other related rules are the hu46 ICRC, The updated Commentary on the First Geneva Convention (2016), para. 190. 47 Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (1977) (Additional Protocol I to the Geneva Conventions), arts. 77, 78; Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of Non-International Armed Conflicts (1977)(Additional Protocol II to the Geneva Conventions), art. 4(3); ICRC, Customary International Humanitarian Law database, rule 135 on children, https://ihl-databases.icrc.org/ customary-ihl/eng/docs/v1_rul_rule135. mane treatment for detained persons, including detained children,48 the respect for family life as much as possible,49 and the right of detained persons to correspond with their families.50 International refugee law 34. The 1951 Convention relating to the Status of Refugees and its 1967 Protocol, along with regional refugee instruments,51 are the core legal instruments of the international refugee regime, complemented by customary international law and international human rights law. These instruments define the term “refugee”52 and establish an international framework for the protection of refugees, setting out the obligations of States towards refugees on their territory or otherwise under their jurisdiction, and the basic minimum standards of treatment for individuals defined as refugees. The principle of non-refoulement is the cornerstone of international refugee protection. Enshrined in article 33 (1) of the 1951 Convention, the principle provides that a refugee may not be expelled or 48 Geneva Conventions of 12 August 1949, common art. 3; Additional Protocol II to the Geneva Conventions, art. 5; ICRC, Customary International Humanitarian Law database, rule 87 on humane treatment, https://ihl-databases.icrc.org/ customary-ihl/eng/docs/v1_rul_rule87. 49 See, among other things, Geneva Convention (IV) relative to the Protection of Civilian Persons in Time of War (1949), art. 27; ICRC, Customary International Humanitarian Law database, rule 105 on respect for family life, https://ihl-databases.icrc.org/customary-ihl/eng/docs/v1_rul_rule105. 50 See, among other things, Geneva Convention (IV) relative to the Protection of Civilian Persons in Time of War (1949), arts. 106 and 107; Additional Protocol II to the Geneva Conventions (1977), art. 5 (2) (b); Convention on the Rights of the Child (1989), art. 37 (c); ICRC, Customary International Humanitarian Law database, rule 125 on correspondence of persons deprived of their liberty, https://ihl-databases.icrc. org/customary-ihl/eng/docs/v1_rul_rule125. 51 African Union Convention Governing the Specific Aspects of Refugee Problems in Africa (1969); Cartagena Declaration on Refugees (1984). 52 Convention relating to the Status of Refugees (1951), art. 1A. 21.