http://www.icrc.org/Web/eng/siteeng0.nsf/htmlall/5LPHBV/%24File/irrc_849_Dorman.pdf

A textual interpretation of the Conventions can only lead to the conclusion
that all persons who are not protected by GC I-III, thus also persons
who do not respect the conditions which would entitle them to POW status/
treatment, are covered by GC IV provided that they are not:
• nationals of a State which is not party to the Convention;
• nationals of the Party/Power in which hands they are; or
• nationals of a neutral State (only if they are in the territory of a belligerent
State) or co-belligerent State with normal diplomatic representation
(for details see the foregoing quotation from the ICRC Commentary).