The Britain-based Syrian Observatory for Human Rights said at least 44 people were killed on December 22 in air strikes by government helicopters on the city of Aleppo.
The observatory said helicopters dropped "barrel bombs" -- barrels packed with explosives -- on several Aleppo neighborhoods under rebel control.
The Aleppo Media Center, a network of citizen journalists, reported one bomb hit a bus, killing everyone on it.
Human Rights Watch released a report on December 21 claiming "government forces have been wreaking disaster on Aleppo" for the last month.
Earlier on December 22, a suicide car bombing near a school in the Syrian province of Homs killed at least 12 people.
The bomber detonated an explosive-laden car near a school in the Shi'ite town of Umm al-Amed.
The observatory said at least six of those killed were schoolchildren.
Based on reporting by AFP and AP