White phosphorus can be used though , its not banned
"White phosphorus munitions are not banned under international law, but because of their incendiary effects, their use is supposed to be tightly regulated.[57] Because white phosphorus has legal uses, shells filled with it are not directly prohibited by international humanitarian law. Experts consider them not as incendiary, but as masking, since their main goal is to create a smoke screen.[58]"
https://en.wikipedia.org/wiki/White_phosphorus_munition