Syria's state news agency said an "armed terrorist group" assassinated a high-ranking air force general. Maj. Gen. Abdullah Mahmoud al-Khalidi was gunned down while getting out of his car in the mostly Kurdish neighborhood of Rukn Eddine in Damascus.
The government views the rebels as terrorists and accuses them of being foot soldiers in a foreign plot to destroy Syria.
In Turkey, Foreign Minister Ahmet Davutoglu expressed "great sadness" that the cease-fire had failed and said government was done talking to Assad's regime.
"Unfortunately the attacks continued, and the Syrian people spent the holidays suffering great pain," Davutoglu told reporters in Ankara. "There would be no meaning to forging a dialogue with a regime that pressed ahead with such a massacre even during the holidays."
Associated Press writer Suzan Fraser in Ankara, Turkey, and Bassem Mroue in Beirut contributed reporting.