Norma relacionada
France
Practice Relating to Rule 145. Reprisals
Section B. Reasonable notice and measure of last resort
France’s LOAC Manual (2001) states that reprisals must always be preceded by a warning. 
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. 109.
At the CDDH, France made a proposal for a draft article on reprisals within the 1977 Additional Protocol I – which it later withdrew – which read, inter alia, as follows:
2.… The prohibition [of the taking of reprisals] may be waived on condition:
(a) that the Party victim of the breach clearly has no means of putting an end to the breach other than by considering recourse to reprisals,
(c) that the Party responsible for the violation shall be given due warning that such measures will be taken if the violation is continued or renewed. 
France, Draft Article 74 bis Additional Protocol I submitted to the CDDH, Official Records, Vol. III, CDDH/I/ 221, 19 February 1975, p. 323.
At the CDDH, France made another proposal for a draft Article on reprisals within the 1977 Additional Protocol I – which it later withdrew – which read, inter alia, as follows:
2.The measures [which are designed to repress the breaches of and induce compliance with the Protocol] may be taken only when the following conditions are met:
(a) The measures may be taken only when other efforts to induce the adverse Party to comply with the law have failed or are not feasible, and the victimized Party clearly has no other means of ending the breach;
(c) The Party committing the breach must be given specific, formal, and prior warning that such measures will be taken if the breach is continued or renewed. 
France, Draft Article 74 bis Additional Protocol I submitted to the CDDH, Official Records, Vol. III, CDDH/I/ 221/Rev.1, 22 April 1976, p. 324.