Geneva Convention, Protocol I Art 43.1
Among the legitimate categories of combatants in a conflict, Additional Protocol I identifies the members of “all organized armed forces, groups and units which are under a command responsible to a party [to the conflict] for the conduct of its subordinates.” This applies even to parties represented by a government or authority that is not recognized by an adverse party (API Art. 43.1). This provision introduces the possibility of applying Additional Protocol I to conflicts in which government forces are opposed to resistance or national liberation movements.
UNGA resolution 37/43
the legitimacy of the struggle of peoples for independence, territorial integrity, national unity and liberation from colonial and foreign domination and foreign occupation by all available means, including armed struggle
UN Resolution 3246
Affirms the legitimacy of armed resistance by oppressed peoples in pursuit of the right to self-determination, and condemns governments which do not support that right
