Barrel bomb attacks throughout Syria have killed more than 20,000 people since the conflict began in March 2011, according to a December 2013 statement by the opposition Syrian National Council (SNC).[33] It is estimated that, as of mid-March 2014, between 5,000 and 6,000 barrel bombs have been dropped during the war and their use has escalated.[34] Aleppo has been the focal point of the Syrian government's use of barrel bombs.[35] Over time, government forces have refined their use of the barrel bomb to cause maximum damage - dropping one device and then waiting 10 to 30 minutes to drop another bomb on the same location.