The invention provides aqueous thermosetting binder compositions exhibiting both of improved flame retardation and wet tensile strength comprising a reducing sugar, a diprimary diamine or a polyprimary diamine, a phosphorus acid salt and from 3 to 20 wt. %, based on total solids, of an aqueous polymeric polyacid solution polymer containing phosphorus or its salt, wherein the aqueous thermosetting binder composition comprises from 0.7% P (s/s) to 5% P (s/s).