Syrian military helicopters dropped more improvised “barrel bombs” on the northern city of Aleppo on Sunday, a monitoring group said, bringing the death toll to at least 83 people in the latest episode of a campaign many consider a war crime.

Most of the victims killed since Friday have been civilians from the city’s eastern districts, including women and children, according to the British-based Syrian Observatory for Human Rights, which has a broad network of sources across Syria.

The use of barrel bombs – oil drums or cylinders packed with explosives and metal fragments – has drawn international condemnation, including from Syria’s opposition delegation and their Western backers at recent peace talks in Switzerland.