Related Rule
France
Practice Relating to Rule 99. Deprivation of Liberty
Section A. General
France’s LOAC Summary Note (1992) provides that “illegal detention” is a grave breach of the 1949 Geneva Conventions. 
France, Fiche de Synthèse sur les Règles Applicables dans les Conflits Armés, Note No. 432/DEF/EMA/OL.2/NP, Général de Corps d’Armée Voinot (pour l’Amiral Lanxade, Chef d’Etat-major des Armées), 1992, § 3.4.
France’s LOAC Teaching Note (2000) provides: “Protected persons shall not be detained arbitrarily.” 
France, Fiche didactique relative au droit des conflits armés, Directive of the Ministry of Defence, 4 January 2000, annexed to the Directive No. 147 of the Ministry of Defence of 4 January 2000, p. 5.
France’s LOAC Manual (2001) provides under the heading “Interned persons”:
Decisions on internment are taken by military or administrative authorities, whereas decisions on detention in principle come under the competence of judicial authorities. The law of armed conflicts does not refer to the internment measures in the case of internal armed conflicts. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 95.