No injuries were reported.
Marat Kulakhmetov, a commander with the Georgia-Russian-Ossetian peacekeeping forces, said it was still unclear who fired first.
The shooting comes one day after assailants attacked police posts in the regional capital, Tskhinvali, injuring three police officers.
The chairman in office of the Organization for Security and Cooperation in Europe (OSCE), Spanish Foreign Minister Miguel Angel Moratinos, expressed concern over the violence.
In a statement today, Moratinos urged all sides to exercise restraint and engage in a "meaningful political dialogue."
(with material from agency reports)