The FBI is investigating a domestic terror attack after two Pennsylvania teenagers allegedly threw viable explosive devices during a New York clash.Suspects Emir Balat and Ibrahim Kayumi face federal charges for deploying shrapnel-filled triacetone triperoxide bombs during an anti-Islam rally.One individual associated with the far-right organizers was arrested for pepper-spraying counter-demonstrators while a suspect reportedly shouted religious slogans.Federal authorities confirmed the devices were lethal and capable of mass casualties after executing search warrants in Pennsylvania and New Jersey.