Syrian activists say government helicopters have dropped barrel bombs in a neighborhood in the northern city of Aleppo, killing at least 15 people.The Britain-based Syrian Observatory for Human Rights says the attack on Tuesday in the city, carved up into rebel- and government-held areas, hit near a bus depot. The group said at least 20 people were killed and 30 were wounded, including women and children.The Local Coordination Committees, another monitoring group, said at least 15 people were killed in the attack on the Jisr al-Haj neighborhood. Both groups are based outside Syria but rely on a network of activists on the ground. The Aleppo Media Center, based in the city, said at least 35 people were killed.Different casualty figures soon after the attacks are not uncommon.