Hey Robert,
I would wager that they are Russian, the mes kit in the foreground is also Russian as are the hoods worn by three of the soldiers (bashlyk), although the ammo pouch on the fellow who is standing is either Austrian or Bulgarian.
Looking closer, the overcoats are not Russian, nor do they look Bulgarian and the Kabalak cap is based on the Bashlyk, so it is possible that these could be Ottoman troops on the Caucasus front using captured weapons and equipment.
Best
Gus