Gunfire shots were heard around the embattled city and smoke could be seen rising from buildings.
Syria's air force dropped barrel bombs, which are explosives stuffed into barrels, and fired missiles on rebel strongholds, as rebels attacked government positions.
The four-day truce that was supposed to go into effect Friday on the beginning of the four-day Muslim feast Eid al-Adha has since been abandoned.
The failure to honor the four-day truce suggests that the violence that has dragged on for over 19 months will continue and might even draw in neighbors such as Turkey, Lebanon, and Jordan.
"This conflict has now taken a dynamic of its own which should be worrying to everyone," said Salman Shaikh, director of the Brookings Doha Center think tank.
Activists say at least 110 people were killed in Sunday's violence.
The Associated Press contributed to this report.
