Related Rule
Cameroon
Practice Relating to Rule 33. Personnel and Objects Involved in a Peacekeeping Mission
Cameroon’s Instructor’s Manual (1992) states:
It is prohibited for belligerents to open fire on interposition forces and on their materiel, [as] these forces’ mission is not to fight one or the other party to the conflict (except in case of self-defence) but to interpose themselves between such parties in order to ensure respect for a cease-fire. 
Cameroon, Droit international humanitaire et droit de la guerre, Manuel de l’instructeur en vigueur dans les Forces Armées, Présidence de la République, Ministère de la Défense, Etat-major des Armées, Troisième Division, Edition 1992, p. 110.
Cameroon’s Instructor’s Manual (2006) states:
Conduct with regard to intervention forces
It is prohibited for belligerents to open fire on intervention forces and their objects. Intervention forces are those whose mission is to intervene in order to ensure respect for a cease-fire with the aim of eventually ending the conflict, rather than to combat one or other of the parties to the conflict (except in case of self-defence). 
Cameroon, Droit des conflits armés et droit international humanitaire, Manuel de l’instructeur en vigueur dans les forces de défense, Ministère de la Défense, Présidence de la République, Etat-major des Armées, 2006, p. 257, § 612.