A temporary truce between warring parties in Syria collapsed on Friday just hours after it began, with the army and rebels each accusing the other of violating the Muslim holiday four-day ceasefire.
State television blamed "terrorists," the regime term for rebels, for a car bombing in the capital that killed at least five people and wounded more than 30.
And rebels accused regime forces of opening up with artillery in the embattled north.
The army said it was responding to attacks by armed rebels that violated the truce agreed to mark Eid al-Adha, one of the most sacred holidays in Islam, which started at dawn.
"Armed terrorist groups attacked military positions, thereby clearly violating the halt to military operations agreed by the army command," the military said in a statement read on state television.
"Our valiant armed forces are responding to these violations and pursuing these groups," the military added.
A commander of the main rebel group, the Free Syrian Army (FSA), in the northern city of Aleppo accused the regime of breaking their pledge to hold its fire.
"The regime does not respect the ceasefire, it is not shooting and there are no clashes but it has started shelling... What ceasefire? We can't trust the regime," said Abd al-Jaber al-Akaidi.
"The regime is perfidious, a cheater and a liar," he said.
President Bashar al-Assad's forces and the FSA had agreed to a call by UN-Arab League peace envoy Lakhdar Brahimi to lay down their arms for the four-day duration of Eid.
But as the day progressed, reports of violations nationwide showed there had been little let-up in the violence.
The Syrian Observatory for Human Rights reported that dozens of people were killed or wounded in the car bombing that rocked a southern area of Damascus.
"The explosion of a booby-trapped car outside the Omar bin Khattab mosque in the area known as Shorta in the Daf Shawk district killed and wounded dozens of people," the Britain-based rights watchdog said.
State television said at least five people were killed and 32 wounded, calling the attack a "terrorist" act.
A security source told AFP that the bombing had targeted residential buildings for police officers and their families and that children were playing in the area when the blast occurred.
The Syrian Observatory confirmed five deaths and more than 30 wounded, adding that children were among the casualties.
The rebel jihadist group Al-Nosra Front, which has claimed responsibility for deadly car bombings, has categorically rejected any truce.
The Observatory also reported that 11 Syrian soldiers were wounded in a car bombing in Daraa.
Daraa is the cradle of the anti-regime revolt that erupted in mid-March 2011 as a peaceful uprising but developed into an insurgency in the face of brutal state repression, killing an estimated 35,000 people.
The Observatory said the truce had "collapsed" in several regions and gave an initial death toll of 47 on Friday, a day after 135 were reported killed.
-- Assad joins Eid prayers --
Observatory director Rami Abdel Rahman reported fighting in various parts of Syria, including in and around Damascus, in second city Aleppo, in the central city of Homs and near the Wadi Deif military base in the northwest.
At least 10 soldiers and four rebels were killed at Wadi Deif, the watchdog said.
The Observatory relies on a countrywide network of activists and medics in civilian and military hospitals, and its tolls take into account civilian, military and rebel casualties.
Regime forces and the FSA said on Thursday they would heed Brahimi's call for the temporary ceasefire, but both also reserved the right to respond to aggression.
An AFP reporter who toured the Aleppo region on Friday morning said the area appeared peaceful and in some neighbourhoods children were playing, wearing new clothes and eating sweets.
Some families were also travelling to check on their homes on the front line, taking advantage of an early morning lull, the reporter said.
Brahimi is hoping that a temporary truce could pave the way for a more permanent ceasefire during which he could push for a political solution to the 19-month conflict and bring aid to the most stricken regions.
Before the latest violence, Arab League deputy chief Ahmed Ben Hilli told AFP in Cairo the truce was "being respected according to initial indications" and it could be followed by a longer ceasefire and a proposal to deploy UN peacekeepers.
After clashes late Thursday, the ceasefire began as morning prayers marked the Eid al-Adha feast at the end of the hajj pilgrimage. State television showed Assad at a Damascus mosque, smiling and chatting with worshippers.
But the ceasefire was also tested as security forces opened fire at anti-regime protests that followed the prayers.
Protests took place in Damascus and its suburbs, in Aleppo, in the northeast in Deir Ezzor and Raqa and at several towns in Daraa province, according to activists and the Observatory.
At Inkhel in Daraa, police used gunfire to disperse protesters, wounding three people, said the Observatory.
General Mustafa al-Sheikh of the FSA said the rebels considered the protest crackdown a violation of the ceasefire but were not planning to respond.
"Preventing demonstrations by opening fire is a violation of the ceasefire. But we are showing more restraint than the regime because for the moment we want to give the ceasefire a chance," he told AFP by telephone from Turkey.
Aleppo residents said they were taking little joy in the Eid holiday despite the lull.
"Although there was no gunfire this morning, there was nothing that made it feel like Eid today," said restaurant owner Hany, 35.
A soldier in the Old City of Aleppo said he would have to stay on guard. "I heard about the ceasefire on television but my duty is to stay alert to stop the rebels from moving forward," he said.