The UN's Syria envoy, Staffan de Mistura, on Monday condemned as "unacceptable" the weekend bombings at a rebel-held town outside Damascus that killed nearly 100 people.
"The government's bombing of (Douma) yesterday is devastating," de Mistura said. "Hitting crowded civilian markets killing almost one hundred of its own citizens by a government is unacceptable in any circumstances."
Sunday's series of air strikes on Douma was one of the bloodiest regime attacks in Syria's four-year civil war.
De Mistura said Sunday's attacks underscored the need to resume political dialogue to end the conflict that has claimed more than 240,000 lives.
"This conflict will have no military solution, as has been proven over the recent years," de Mistura said in a statement.