In connection with the US withdrawal from Afghanistan, a drone attack was carried out against what the US military then stated was a suicide bomber in Kabul.
Now, General Kenneth McKenzie says that all those killed in the August 29 attack - ten in total, seven of them children - were civilian victims.
Nine of them belonged, according to US data, to the same family.
"Tragic mistake"
"The attack was carried out with a genuine conviction that it would stop an imminent threat to our soldiers and those who were evacuated, but it was a mistake," McKenzie said according to CNBC.
He says he is responsible for what he calls a "tragic mistake".
The investigation finds that a surveillance drone at the airport saw how men loaded suspicious goods in a car.
But what was suspected to be bombs turned out to be containers of drinking water.
McKenzie says that "it is unlikely" that anyone in the family, which consisted of nine people, had any connection with the terrorist movement IS in Afghanistan.
Official apology
Secretary of Defense Lloyd Austin also made an official apology:
My deepest condolences to the surviving family members of those killed.
We apologize and we will make every effort to learn from this terrible mistake. "
The drone attack on the car with civilians came days after a bomb detonated outside the airport in Kabul on August 26 during the ongoing evacuation.
More than 180 people were killed in the attack, of which nearly 170 were Afghans trying to secure security for evacuation.
13 US soldiers were killed in the attack.
Friday's unanimous apologies from Washington came after days of media reviews of the incident in Kabul.