( CNN ) -- A Syrian army helicopter dropped barrel bombs on a vegetable market in Aleppo on Thursday , killing 24 people , opposition activists said . Dozens more were injured in the attack on the opposition-held town of Atareb , according to the Local Coordination Committees of Syria . Barrel bombs , which are drums packed with explosives and shrapnel , can level entire buildings with one hit . Rescue efforts were under way as volunteers used bulldozers to clear wreckage and remove the rubble of the bombed buildings , according to the opposition . It posted purported videos of the attacks on social media . Another airstrike targeted the nearby village of Tal Rifaat , the group said . CNN can not independently verify the authenticity of the reports or the videos . The attack comes days after several U.S. officials said the Syrian government may have used chlorine gas in a deadly attack on its people . State Department spokeswoman Jen Psaki said the United States `` had indications of the use of a toxic industrial chemical , probably chlorine , in Syria this month in the opposition-dominated village of Kfar Zeita . '' If true , a chlorine attack would undermine a deal brokered by Russia last fall and approved by the U.N. Security Council that requires Syria to surrender its chemical weapons to the international community . The Syrian opposition does not have helicopters to carry and deliver such weapons , and has been trading accusations about the April 11 chlorine incident with the government . The United Nations says more than 100,000 people have been killed in Syria since the opposition launched anti-government protests in 2011 .
Barrel bombs are drums packed with explosives and fuel . They can destroy entire buildings with one hit . Days earlier , Iraqi officials accused ISIL of using chlorine gas in a deadly attack .