Government war planes bombed opposition-held areas of Syria and President Bashar al-Assad's forces and rebels fought on the outskirts of the capital Damascus on New Year's Day on Tuesday.
A year ago, many diplomats and analysts predicted Assad would leave power in 2012. But despite international pressure and rebel gains, he has proved resilient.
His inner circle remains largely intact and retains control of the armed forces, even if it relies on air strikes and artillery power to hold back the rebels fighting to overthrow him.
The air force pounded Damascus's eastern suburbs on Tuesday and rebel-held areas of Aleppo, the second city and commercial capital, as well as several rural towns and villages, opposition activists said.
Opposition video posted on the Internet showed plumes of grey smoke rising in Irbin, in the east of Damascus.
Residents of the capital began the new year to the boom of artillery hitting southern and eastern outskirts, which form a rebel-held arc around the capital. The heart of the city is still firmly under government control.
In the city center, soldiers manning checkpoints fired celebratory gunfire at midnight although the streets were largely deserted.
"How can they celebrate? There is no 'Happy New Year'," Moaz al-Shami, an opposition activist who lives in central Mezzeh district, said over Skype.
He said rebel fighters attacked one checkpoint in Berzeh district on Tuesday morning. Opposition groups said mortar bombs hit the southwest suburb of Daraya, which the army attacked on Monday to retake it from rebels.
An estimated 45,000 people have been killed in the conflict, which started in early 2011 with peaceful protests demanding democratic reforms but turned into an armed uprising after months of attacks on protesters by security forces.
A resident of the central city of Homs said artillery shelling had smacked into its Old City on Tuesday.
Homs lies on the north-south highway and parts of the ancient city have been leveled during months of clashes. Government forces ousted rebels from Homs early last year but militants have slowly crept back in.
"The Old City is under siege. There is shelling from all sides," said the resident, who asked to remain anonymous.
A video posted on YouTube showed the bodies of three boys who activists said were arrested at a government checkpoint on their way home from school in Damascus' Jobar suburb on Sunday.
One of the boys, who appear to have barely reached adolescence, has his hands tied behind his back. Another had a large open wound on his throat.
Reuters could not independently verify the reports and the footage.
The opposition-linked Syrian Observatory for Human Rights, a British-based monitoring group, reported 160 people killed on the final day of 2012, including at least 37 government troops.
The civil war in Syria is the longest and deadliest of the conflicts that rose out of the uprisings that have swept through the Arab world over the past two years.
Many Sunni Muslims, the majority in Syria, back the rebellion, while Assad, a member of the Shi'ite-derived Alawite minority sect, is backed by some minorities who fear revenge if he falls. His family has ruled Syria since his father seized power in a coup 42 years ago.
Assad's forces now rely more on air strikes and artillery bombardment rather than infantry. Residential areas where rebels are based have been targeted, killing many civilians.
Rebels have taken swathes of the northern mountains and eastern desert but have struggled to hold cities, saying they are defenseless against Assad's Soviet-equipped air force.
Diplomatic efforts to end the war have failed, with the rebels refusing to negotiate unless Assad leaves power and the president pledging to fight until death. Western and Arab states have called for him to go. He is backed by Russia and Iran.
In the last days of 2012, international mediator Lakhdar Brahimi called on countries to push the sides to talk, saying Syria faced a choice of "hell or the political process".
One Damascus resident, who asked not to be identified for security reasons, said the usual New Year's Eve crowds were absent from the increasingly isolated capital.
"There was hardly anyone on the streets, no cars, no pedestrians. Most restaurants, cafes and bars were empty," she said.
Some young people gathered at three bars in the old city.
"There was music but nobody was dancing. They just sat there with a drink in their hands and smoking. I don't think I saw one person smile," she said.
The midnight gunfire caused alarm.
"It was very scary. No one knew what was going on. People got very nervous and started making phone calls. But then I discovered that at least on my street, the gunfire was celebratory."