At least 18 civilians were killed in a single regime barrel bomb attack in Syria's northern city of Aleppo on Thursday, a monitoring group said.
The Syrian Observatory for Human Rights said the bomb, dropped from a helicopter, struck an eastern sector of the divided city where people were gathering to buy and sell fuel.
In the northern province of Idlib, seven civilians were killed in a regime air strike near a school, Rami Abdel Rahman, the head of the Britain-based Observatory, told AFP.
The deaths came after UN envoy Staffan de Mistura dispatched a delegation to Aleppo in efforts to freeze fighting there.
On Sunday, a rebel coalition rejected his plan, saying that, among other problems, it did not address the "regime's use of... barrel bombs prohibited by the international community".
The government has regularly dropped barrel bombs on opposition areas across the country, particularly rebel-held parts of Aleppo province.
Rights groups have criticised the bombs -- crudely constructed from barrels packed with explosives -- as indiscriminate, citing the large number of civilians they kill.
Assad has denied the army uses them.