In the northeastern suburbs of Damascus, regime forces killed scores of rebels in an ambush early Sunday.
State-run news agency SANA did not give a number but said the army in Adra "eliminated a number of terrorist members of Jabhat al-Nusra trying to infiltrate" suburbs near the capital, a reference to an al-Qaida affiliated rebel group.
The Observatory confirmed the ambush in Adra, saying at least 28 rebels were killed and many others were missing.
It said an elite Republican Guard officer who led the ambush was also killed.
Also Sunday, activists reported rare fighting between rebels and regime forces in the coastal province of Tartus, a stronghold of Assad's minority Alawite sect.
The Observatory accused the regime of killing 13 members of the same family, including four women and six children, in an attack in the Sunni Muslim village of Bayda following the clashes.
The village is predominantly Sunni but is located in the Alawite ancestral heartland. It was the site of a mass killing in May.
Syrian state television claimed that a pro-government group hacked into two social messaging networks and seized records of local users.
That could expose Syrian rebels and other activists who depend on the networks to publicize army crackdowns on their hometowns and communicate with each other. Many telephone landlines and cellphones in Syria are assumed to be tapped.