https://en.wikipedia.org/wiki/White_phosphorus_munitions#International_lawArticle 1 of Protocol III of the Convention on Certain Conventional Weapons defines an incendiary weapon as “any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or combination thereof, produced by a chemical reaction of a substance delivered on the target”. Article 2 of the same protocol prohibits the deliberate use of incendiary weapons against civilian targets (already forbidden by the Geneva Conventions)