Almost 150 people died on the first day of a barely-observed truce between the warring parties in Syria, a watchdog said, adding that a fresh clashes on Saturday claimed more lives.
The Syrian Observatory for Human Rights said of the 146 people killed in bombings, artillery fire and fighting on Friday, 53 were civilians, 50 were rebels and 43 were members of President Bashar al-Assad's forces.
State media blamed "terrorists," the regime term for rebels, for a car bomb attack in Damascus that killed at least eight people and wounded 30, and a rights watchdog reported another deadly bombing farther south in Daraa.
Rebels accused regime forces of opening up with artillery in the embattled north, where the Syrian Observatory for Human Rights reported fighting near the key army base of Wadi Deif and shelling and clashes near Damascus.
The army said it was responding to attacks by rebels who violated the truce agreed to mark Eid al-Adha, one of the most sacred holidays in Islam, which started at dawn.
UN and Arab League envoy Lakhdar Brahimi had brokered the ceasefire in the hope that if successful, it could lead to a longer cessation of violence.
President Bashar al-Assad's forces and main rebel group the Free Syrian Army (FSA) had both agreed to a call by Brahimi to lay down their arms for the four-day Eid, but both also reserved the right to respond to attacks.
"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," it added.
An FSA commander in the northern city of Aleppo accused the regime of breaking the pledge to stop firing.
"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."
The rebel jihadist group Al-Nosra Front, which has claimed responsibility for deadly car bombings in the past, had refused to sign up to the ceasefire.
As the day progressed it became clear there had been little let-up in the violence.
The Britain-based Observatory reported car bombings in Damascus and in Daraa, cradle of the anti-regime revolt that has become a fully fledged uprising since it broke out in mid-March last year.
The watchdog said the car bombing outside the Omar bin Khattab mosque of the Daf Shawk district in southern Damascus killed eight people and wounded more than 30, with children among the casualties.
State television reported at least five dead and 32 wounded in the "terrorist" act.
A security source told AFP the bombing targeted residential buildings for police officers and their families, and that children were playing in the area when the blast occurred.
In Daraa, three soldiers were killed and eight wounded when a car bomb exploded near a military checkpoint and the railway station, the Observatory said. Eight troops were wounded, most of them critically.
The Observatory said the truce had "collapsed" in several regions and gave a death toll of 81 on Friday, a day after 135 were reported killed, adding to an estimated death toll of 35,000 people over 19 months of conflict.
Observatory director Rami Abdel Rahman reported fighting in various areas, including in and around Damascus, in second city Aleppo, in the central city of Homs and near the Wadi Deif base in the northwest.
At least 10 soldiers and four rebels were killed at Wadi Deif, the watchdog said.
It also reported army shelling on the northern Damascus suburb of Douma and the town of Harasta near the capital where a man died as troops and rebels clashed.
The Observatory relies on a countrywide network of activists and medics in civilian and military hospitals, and says its tolls take into account civilian, military, and rebel casualties.
In Aleppo, scene of fierce fighting since mid-July, there was a brief morning respite with children playing in the streets of some neighbourhoods, an AFP reporter said.
Some families also took advantage of the lull to check on their homes on the front line.
Residents reported clashes at midday after rebels tried to overrun a checkpoint near the Mohasab army base in the northeast Seryan district, and in the Sheikh Maqsud area between Kurdish militias and rebels.
The Observatory said nine fighters were killed in the clashes between rebels and Kurdish militants.
Shams, a mother in the city's army-controlled Sabil district, called the ceasefire "only a political phrase and not a reality on the ground."
Brahimi had hoped the truce might lead to a more permanent ceasefire during which he could push for a political solution and bring aid to stricken areas.
After clashes late Thursday, the ceasefire began as morning prayers marked Eid al-Adha, the Feast of Sacrifice capping the end of the annual hajj pilgrimage to Mecca.
State television showed Assad at a Damascus mosque, smiling and chatting with worshippers.
The truce was also tested as security forces opened fire to disperse anti-regime protests after prayers at Inkhel in Daraa, wounding three people, the Observatory said.
General Mustafa al-Sheikh of the FSA said the rebels considered the protest crackdown a ceasefire violation, but they were not planning to respond.