Afghan security forces and their American-led international allies have killed more civilians so far this year than the Taliban have, the United Nations said in a report on Tuesday, once again raising alarm that ordinary Afghans are bearing the brunt of an increasingly deadly 18-year war. In the first six months of the year, the conflict killed nearly 1,400 civilians and wounded about 2,400 more. Afghan forces and their allies caused 52 percent of the civilian deaths compared with 39 percent attributable to militants mostly the Taliban, but also the Islamic State. The figures do not total 100 percent because responsibility for some deaths could not be definitively established. The higher civilian death toll caused by Afghan and American forces comes from their greater reliance on airstrikes, which are particularly deadly for civilians. The United Nations said airstrikes resulted in 363 civilian deaths and 156 civilian injuries. The United Nations report comes as both sides try to increase their battlefield leverage amid continuing peace negotiations in Doha, Qatar, between the United States and the Taliban. The United Nations report said 83 percent of casualties from airstrikes were attributed to international military forces, essentially pointing the finger at the United States military, which is the only member of the international coalition in Afghanistan that carries out airstrikes. The Afghan Air Force was responsible for about 10 percent. Fourteen American soldiers have died in Afghanistan so far this year.