An August U.S. drone strike in Kabul that killed 10 civilians was not caused by criminal negligence but by a series of errors, including not noticing a child minutes before the strike took place, an investigation by a military inspector general found on Wednesday.

The August 29 strike killed 10 civilians, including seven children, in an incident the military previously called a "tragic mistake."

An investigation by the Air Force inspector general said the strike was caused by execution errors, interpreting information that supported certain viewpoints, and communication breakdowns.

"It's a regrettable mistake. It's an honest mistake," Lieutenant General Sami Said, the Air Force inspector general, told reporters.