Related Rule
Practice Relating to Rule 6. Civilians’ Loss of Protection from Attack
Belgium’s Teaching Manual for Soldiers states: “A civilian who takes up arms logically loses the protection granted to civilians and may be attacked.” 
Belgium, Droit de la Guerre, Dossier d’Instruction pour Soldat, à l’attention des officiers instructeurs, JS3, Etat-Major Général, Forces Armées belges, undated, p. 14.
In an explanatory memorandum submitted to the Belgian Parliament in 1985 in the context of the ratification procedure of the Additional Protocols, the Belgian Government stated: “The condition [for civilian immunity from attack], however, is that they do not participate directly in hostilities, which is of course a question of fact.” 
Belgium, House of Representatives, Explanatory memorandum on a draft bill for the approval of the Additional Protocols, 1984–1985 Session, Doc. 1096-1, 9 January 1985, p. 10.