The US ambassador to the UN, Zalmay Khalilzad, has described the killing by security forces in Afghanistan of more than 300 civilians as "unfortunate".
Mr Khalilzad is a former UN envoy in Afghanistan
Mr Khalizad, a former US envoy in Afghanistan, said American and other international troops did their best to avoid hitting civilians.
"But sometimes it happens that weapons go awry, and war is not a perfect science, unfortunately," he said.
He also accused Taleban fighters of using civilians as human shields.
Mr Khalilzad said that civilian deaths in Afghanistan should be investigated and that "lessons are learned from those investigations".
He was speaking to reporters in Rome, where the Italian government is hosting a two-day conference on how to strengthen the rule of law in Afghanistan.
Afghan President Hamid Karzai is due to speak on Tuesday, along with United Nations Secretary-General Ban Ki-moon.
Mr Karzai recently accused foreign forces of "reckless" attacks in Afghanistan.
He has ordered a more thorough investigation into air raids in Helmand province last week.
Afghan sources say a total of 45 civilians and 62 Taleban fighters died in Friday's strike but US-led coalition forces and Nato question the figure.
Last week Mr Karzai said the foreign forces were killing civilians with an "extreme use of force" and were not co-ordinating properly with the Afghan government.
Nato forces say they welcome the investigation.