Government forces are also battling rebels in Damascus' outskirts including the eastern suburb of Mleiha, which saw heavy fighting on Saturday.
"Two citizens were martyred and eight others wounded ... by mortars fired by terrorists at the opera house in the Abbassin area in Damascus," a report on state news agency SANA said on Sunday. It did not what day this happened.
President Bashar Assad's forces are in control of central Damascus but rebels have been able to launch mortar and rocket attacks into the city's centre, sometimes hitting heavily-secured upscale districts and embassy grounds.