Yeah, the US has not signed a number of things that forbid various weapons, including explosive rounds, cluster bombs, poison gases and the like. It still conforms to most of them, probably out of political convenience, but it has been known to use incendiary-explosive rounds against personnel (the infamous .50 Raufoss rounds), though in a very limited fashion (basically, snipers engaging targets of opportunity with anti-materiel rifles). There were also cases of dropping incendiaries on personnel in Iraq war (not napalm, as some reported, but pyrogel is even worse than that).