Forces loyal to Syrian President Bashar al-Assad have killed thirteen civilians and injured dozens on Saturday in a barrel bomb attack in Deraa city of southwestern Syria, according to medical sources.The sources told Anadolu Agency that the attack killed everyone from a family of nine. The death toll also included a number of children and women, sources said.A Civil Defense Volunteers team rushed to the area to rescue victims stuck under collapsed buildings.Barrel bombs are improvised explosives typically consisting of a barrel filled with high explosives, shrapnel, oil or chemicals, which is then dropped from an aircraft. Although their usage has been prohibited, the monitoring groups have claimed that Assad regime continues to use barrel bombs against civilians.More than 220,000 people have been killed in Syria since the conflict between Bashar al-Assad's regime and opposition forces began in 2011, according to the United Nations.