The human rights observers said children were among the victims in a bomb blast near a playground and a mosque in Damascus.
The observers also reported fighting between rebels and soldiers in several areas around the country, including a Damascus suburb and the Wadi al-Daif army base.
Syrian army officials said soldiers were responding to cease-fire violations by the rebels, while opposition fighters accuse the army of breaking the truce.
United Nations special envoy Lakhdar Brahimi arranged the cease-fire so Syrians on all sides could celebrate Eid al-Adha, the holiday marking the end of the Hajj pilgrimage to Mecca.
Syrian television showed President Bashar al-Assad mingling with worshippers at Friday prayers, while some ordinary Syrians said they were just trying to stay alive and were in no mood to celebrate.
