The Syrian capital Damascus has been hit by a car-bomb attack, shattering a four-day ceasefire that had begun hours earlier to mark an Islamic holiday.
Activists said the device exploded near a playground in Daf al-Shouk, a residential area in southern Damascus.
State TV reported five people had been killed and more than 30 wounded, with children among the casualties.
The UN-brokered ceasefire began at 06:00 (04:00 GMT), but fighting has continued across the country.
The truce, to mark the Eid al-Adha holiday, was proposed by UN envoy Lakhdar Brahimi, who hoped it would lead to a peace process.
Both rebels and the army had said they would observe the truce only if the other side held their fire.
By Friday evening, UK-based activist group Syrian Observatory for Human Rights (SOHR) said at least 60 people had been killed throughout the country.
The daily death toll reported by activist groups has regularly exceeded 150 in recent weeks.
The BBC's James Reynolds on the Turkey-Syria border says fighting went on throughout the day near the frontier.
The SOHR, one of the most prominent groups monitoring Syrian casualties, reported various outbreaks of violence in Damascus, Homs and Idlib.
The group said fighting broke out four hours after the ceasefire began at a military base near Maaret al-Numan town, close to the main road between Damascus and Aleppo.
Later, a car-bomb attack in the southern city of Deraa killed three soldiers, said the observatory.
The group says its reports are impartial. However, its information cannot be independently verified.
The car bomb in Damascus appears to have wrecked any lingering chance that the truce might take hold.
Footage of the aftermath showed several destroyed vehicles lying among rubble from badly damaged buildings.
State media blamed the attack on "terrorists".
Activists said the bombing appeared to target civilians in a largely Sunni area where some have supported the uprising against President Bashar al-Assad's government.
Opposition activist group the Local Coordination Committees said crowds had come out to protest against the government after the bombing. Their claims could not be verified.
Other reports claimed there were widespread anti-government protests after Friday prayers.
Demonstrations are now a rare occurrence in Syria, with many protesters fearing for their safety.
According to activists, more than 35,000 people have been killed since the uprising began, while the UN estimates that at least 20,000 have died.
The UN and Arab League have tried several times to broker a ceasefire, but the truces have fallen apart shortly after coming into force.
Mr Brahimi, who acts as envoy for the UN and Arab League, travelled across the Middle East to promote the latest ceasefire plan.
On Wednesday the UN Security Council backed the proposal and expressed hope that it would lead to a broader dialogue.
The Security Council has so far not commented on Friday's violence.