It doesn't look like any weapon I've ever seen.  It may either be fake, or it could be a modified RPG launcher.  One has to question why someone would need to fabricate an RPG launcher when they are relatively plentiful in that part of the world, but the addition of the sniper scope may provide a clue.  Perhaps the insurgents wanted a compact launcher in which they could mount a regular rifle scope instead of the normal PSO RPG scope.  The RPG was designed as an anti-tank weapon, and its optics are designed for targeting armored vehicles.  As armor as advanced, the role of the RPG has changed to more of an anti-personnel role.  Maybe a sniper scope makes more sense for this sort of weapon.  This particular weapon may be more concealable and disposable as well, but that's just a guess.