An opposition monitoring group says at least 14 people, including two young siblings, have been killed in Syria's largest city, Aleppo, as rebels and government forces trade fire.

The Britain-based Syrian Observatory for Human Rights said six people were killed by rebel shelling on government-held areas in the city on Saturday, including the two siblings. Syria's state news agency reported 10 killed, saying rebel-launched rockets struck schools and residential areas.

The Observatory says eight people, including two children, were killed by airstrikes and shelling on the opposition-held side of the city. The activist-run Local Coordination Committees blames the strikes on the government.

The Aleppo Conquest rebel coalition on Saturday threatened to dissolve a nearly two-month-old cease-fire with the government if pro-government forces continued to strike civilians in opposition areas.