In another sign of a growing appetite for original programming on cable television, a leading cable group is adding a third channel to its lineup and stepping up its commitment to original scripted series.

FX Networks, part of News Corporation, will introduce the FXX cable channel on Sept. 2, executives told advertising agency executives and reporters at an upfront presentation in Midtown Manhattan Thursday morning. The presentation was among dozens that channels, networks and newcomers like Crackle, DirecTV and Participant Media are hosting — many earlier than in previous years — before the start of the 2013-14 television season.

FXX, which will be aimed at viewers ages 18 to 34 (and the marketers that seek to reach them), will join two other channels under the FX Networks umbrella at the Fox Cable Entertainment Group: FX, which is aimed at viewers ages 18 to 49, and FXM, for FX Movie Channel, which was formerly known as Fox Movie Channel, aimed at viewers 25 to 54.

Along with the introduction of FXX, FX Networks will also introduce its own version of TV Everywhere, the shorthand term for efforts to make cable programming available beyond cable television to authenticated subscribers who want to watch shows on devices like smartphones and tablets.