At least 15 civilians were killed in a barrel bomb attack on a rebel-held district of Syria's Aleppo city on Saturday, the Syrian Observatory for Human Rights monitor said.The Britain-based group said regime aircraft had dropped two explosive-packed barrel bombs several minutes apart on the Maadi district of eastern Aleppo.The strikes hit "near a tent where people were receiving condolences for those killed this week in the neighbouring district of Bab al-Nayrab," Observatory director Rami Abdel Rahman said."There was a first barrel bomb and when people gathered and the ambulances arrived, a second barrel struck and there were more deaths," an AFP reporter in the rebel-held part of the city said."One ambulance was completely destroyed," he added, citing the local civil defence unit.The Observatory said dozens more were injured in the two strikes and the death toll was expected to rise.Saturday's deadly strikes come after 15 people, among them 11 children, were killed in a barrel bomb attack on Bab al-Nayrab on Thursday.The local Shabha Press news agency said 23 people were killed in Saturday's attack, and published photos showing several of the dead, including a man who appeared to have been riding a motorbike at the time of the strike.Most of his bloodsoaked body lay on one side of the overturned bike, but his severed leg lay on the other side.Once Syria's economic powerhouse, Aleppo city has been ravaged by the conflict that began with anti-government protests in March 2011.The city has been roughly divided between rebel control in the east and government control in the west since mid-2012.Syria's regime has been accused of regularly using barrel bombs -- crude, explosive devices -- on rebel-held areas that are home to civilians.Other parties to the conflict are not known to have used the weapons.