Actually, the Geneva Convention does NOT apply. These "combatants" were captured under arms, while they were not in uniform or carrying identification that they are legal combatants of a country.
IE they fall under the classification of sabotuers, spies, assasins or terrorists. Therefore, they are legally subject to summary military justice, up too and including immediate execution.
I'm not saying thats what should be done, or that we would even consider it under these conditions, but from my military training about the Geneva convention, it would be entirely legal if not appropriate.