© Balazs Gardi Kunar province, Afghanistan. Survivors of a US airstrike.
Afghan authorities announced that the fatalities included four women and a child.
US-led forces said that they fired by mistake on a group of vehicles that carried women and children.
The strikes took place in Uruzgan province on Sunday.
Interior Ministry Spokesman Zemeri Bashary said Monday he had reports of 33 people killed.
He added there were 42 people in the vehicles, all of them civilians.
The Afghan government and NATO have launched an investigation.
Afghan President Hamid Karzai on Saturday criticized foreign troops for killing civilians.
The angry Afghan president held up a picture of an 8-year-old girl whose entire family was killed during a US-led offensive in the southern town of Marjah.
"If a little girl is to collect the dead bodies of family members, you can guess in what situation we are in now," Karzai said.
Many Afghan civilians have been killed both by violent militant acts, including bombings and daily fighting, as well as by US military operations in the country.
... in Washington and feebly attempts to lecture and register anger. Hamid Karzai is only angry because each one of these civilian mass murders - I REFUSE to call them "mistakes" - makes his already tenuous position even worse. The Afghan people do not now or ever liked or trusted him for good reason. He is a traitor to his people - a puppet on a string, dangling to the whims and wishes of the heartless puppeteer. When he welcomed the US to take over and occupy his country for a few dollars more in his pockets, did he actually think they came to bring human rights, democracy, the rule of law and food in the bellies of the Afghan people? No, Americans come to fill bellies with bullets. They come not to enhance brains, but to splatter them all over the terrain - for sport, no less. So now as the few remaining people who support this freak of nature turn against him, he feigns outrage ... as if he has a conscience; as if he has a compassionate bone in his body for the people of Afghanistan. Hamid Karzai is DIRECTLY responsible for these deaths. He collaborates 24/7 with the most terrorist regime on earth.