The four-day truce proposed by UN-Arab League envoy Lakhdar Brahimi already collapsed amid clashes, shelling and car bombings hours after it had been due to take effect with the start of Eid al-Adha holidays on Friday morning.
On the eve of the official end of the ceasefire, the army blamed its failure on "violations" by rebels, who say they have only reacted in self defence.
With hopes shattered of even a temporary halt to the 19 months of bloodshed in Syria, diplomats said Brahimi is looking ahead to new efforts to tackle the crisis.
He is to go to the UN Security Council in November with new proposals to push for talks between President Bashar al-Assad and the opposition, diplomats told AFP, and will head to Russia and China this week to discuss the crisis.
"The political process will not start until Assad and the opposition have battered each other so much that there is no choice. They are not there yet, but Brahimi has some ideas," an envoy at the Security Council said.
On the ground, rebel forces seized three military posts in the Damascus suburb of Douma amid fierce fighting and killed four soldiers at another checkpoint in the region, the Syrian Observatory said.
A car bomb hit the northern Damascus district of Barzeh, wounding around 15 people and causing heavy damage, it said, while another one ripped through Sbeineh, southeast of the capital, without any casualties reported.
Regime warplanes hit the nearby towns of Irbin, Zamalka and Harasta, where the military has been trying for weeks to dislodge rebel forces, the group said.
They also struck a building in the Idlib provincial town of Bara, killing 18 people including eight children and five women, the Observatory said.
At least 99 people were killed nationwide, including 35 soldiers, 34 rebels and 30 civilians, according to a count from the Observatory.
The Britain-based Observatory relies on a countrywide network of activists, lawyers and medics in civilian and military hospitals.
-- Enraged hajj pilgrims curse Assad --
In northern commercial hub Aleppo, fighting broke out in several districts, as the army shelled two neighbourhoods, including the ancient UNESCO-listed souks in the heart of Syria's second city, it said.
In a statement on Sunday, the army said the rebels sought to "destroy" the country.
"The terrorist groups' ongoing, brazen violations to the declared truce are hard proof that they are complicit in the project to shatter and destroy Syria," it said.
It vowed to hit rebels "with an iron fist in order to eradicate them and to save the nation from their evils."
Brahimi had hoped the Eid truce might lead to a more permanent ceasefire to push for a political solution and allow aid to reach stricken areas of the country.
Rights groups say more than 35,000 people have been killed in the conflict, which began as an anti-regime uprising but is now a civil war pitting mainly Sunni rebels against Assad's regime dominated by his minority Alawite sect, an offshoot of Shiite Islam.
In Saudi Arabia's Muslim holy city of Mina, meanwhile, enraged pilgrims cursed Assad and prayed for his death on Sunday as they hurled pebbles at pillars representing Satan in the final ritual of the annual hajj pilgrimage.
Rebel flags billowed among vast crowds of pilgrims headed towards the stoning site amid chanting of anti-Assad slogans.
"O God, may we see Bashar al-Assad soon hanged or burnt, kicked out or a humiliated prisoner," one Syrian yelled through a loudhailer as dozens behind him shouted "Amen."