At least 41 civilians were among the dead as clashes rocked both of the country's largest cities, the Syrian Observatory for Human Rights said.
In the capital, 12 civilians were killed, seven of them by sniper fire, the Britain-based watchdog said. Among them were a couple and their son, gunned down in Bab Tuma, a previously quiet Christian neighbourhood of the Old City.
Two bodies were also recovered from a home in the Midan district of south Damascus, scene of a major counter-offensive by special forces and elite Republican Guards units against rebel fighters earlier in the week.
The Observatory had few immediate details on casualties from what it said were very fierce clashes between troops and rebels in second city Aleppo. It said one rebel fighter had died of his wounds.
The renewed bloodshed came a day after the Security Council added a "final" 30 days to the mandate of the UN Supervision Mission in Syria, tasked with overseeing a ceasefire that was supposed to have taken effect in April but which has been violated daily.
A resolution passed unanimously late Friday said any further extension would only be considered if UN chief Ban Ki-moon "reports, and the Security Council confirms, the cessation of the use of heavy weapons and a reduction in the level of violence sufficient to allow UNSMIS to implement its mandate."
The vote came a day after 302 people were killed in what the Observatory said was the deadliest day of the more than 16-month uprising against President Bashar al-Assad's rule.