Section III, Article 34 of the 1st Geneva Protocol says:
Art. 34. Remains of deceased
1.
The remains of persons who have died for reasons related to occupation or in detention resulting from occupation or hostilities and those or persons not nationals of the country in which they have died as a result of hostilities shall be respected, and the gravesites of all such persons shall be respected, maintained and marked as provided for in Article 130 of the Fourth Convention, where their remains or gravesites would not receive more favourable consideration under the Conventions and this Protocol.
2. As soon as circumstances and the relations between the adverse Parties permit, the High Contracting Parties in whose territories graves and, as the case may be, other locations of the remains of persons who have died as a result of hostilities or during occupation or in detention are situated, shall conclude agreements in order: (a) to facilitate access to the gravesites by relatives of the deceased and by representatives of official graves registration services and to regulate the practical arrangements for such access; (b) to protect and maintain such gravesites permanently; (c) to facilitate the return of the remains of the deceased and of personal effects to the home country upon its request or, unless that country objects, upon the request of the next of kin.
http://www.globalissuesgroup.com/geneva/protocol1.htmledit- but it looks like the US never signed on for this one, as though that would have mattered :-(