Airstrikes on the last major rebel enclave near Damascus have left at least 17 civilians dead, according to the Syrian Observatory for Human Rights.
Footage uploaded to social media purports to show the aftermath of air raids in besieged Eastern Ghouta on Saturday, in which the UK-based monitor reports children were among those killed.
Backed by Russian strikes, government forces have intensified military operations there, tightening a siege that residents and aid workers say uses starvation as a weapon of war, something the regime denies.
Russia rejects claims its jets have killed thousands of civilians since its major intervention two years ago turned the tide in Syria's civil war in favour of President Assad.
Moscow says it only attacks hardline Islamists.
The civil defence rescue service known as the White Helmets, which operates in rebel territory, posted images on Twitter that it said showed the evacuation of civilians after airstrikes in the Eastern Ghouta town of Misraba.
The United Nations says about 400,000 civilians besieged in the area face "complete catastrophe" because aid deliveries by the government are blocked and hundreds of people who need urgent medical evacuation have not been allowed outside the enclave.
Scores of hospitals and civil defence centres in Ghouta and across Syria have been bombed during the conflict in what the opposition says is a "scorched earth policy" to paralyse life in rebel-held areas.