A U.S. airstrike in Afghanistan on Tuesday killed as many as 23 civilians, mostly women and children, according to the United Nations. Investigators say that as many as 10 children and eight women may have been killed in the strike on a compound in Helmand province. The U.S.-led coalition in Afghanistan said Tuesday’s helicopter strike took place amid a firefight between Afghan special forces and Taliban fighters, and that the Taliban had been using the compound “as a fighting position” and accused the militants of using civilians as human shields. A local resident told the BBC that the youngest victim was about 6 years old. The U.N. Assistance Mission in Afghanistan has recorded 649 civilian casualties (dead and injured) as a result of aerial attacks in the first nine months of this year—the highest since records began in 2009. U.S. forces say they are investigating the incident.