Related Rule
Belgium
Practice Relating to Rule 64. Conclusion of an Agreement to Suspend Combat with the Intention of Attacking by Surprise the Adversary Relying on It
Belgium’s Law of War Manual (1983) states: “The denunciation of an armistice for doubtful motives in order to surprise the adversary without giving him the time to prepare could be considered as an act of perfidy.” 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 42.