A US aircraft attacked a Medecins Sans Frontieres (MSF) clinic in the Afghan city of Kunduz because of "human error", a US militaryinquiry said.
The investigation found that the crew of the AC-130 gunship mistook the clinic for a nearby government building that had been seized by Taliban.
At least 30 civilians were killed in the 3 October attack, amid a campaign to retake Kunduz from Taliban forces.
MSF has described the attack was a war crime.
The medical charity disputed initial US justifications for the attack, which said US forces had struck the hospital because they had come under fire in the area.
The US military later admitted that the strike was a mistake and launched an investigation.
On Wednesday, the US commander in Afghanistan, Gen John Campbell, said the investigation had found that the attack on the hospital was "the direct result of avoidable human error, compounded by process and equipment failures".
He said that the crew of the AC-130 plane believed the building was a government compound, the NDS (or National Directorate of Security), which had been taken over by Taliban militants.