Six of the casualties were children. Another two young girls were injured, according to a statement by Afghan president, Hamid Karzai.
The strike took place in Siacha village in Kandahar's Zhari district.
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District governor Niaz Mohammad Sarhadi told Agence France Presse the international forces had been aiming to target Taliban fighters reported to be setting roadside bombs in the area, but missed their target and hit a residential area instead.
President Karzai was "saddened" by the incident and has sent a team to investigate, his statement said.
NATO forces have also sent an assessment team to the site, a spokesperson told AFP.
The representative confirmed to the BBC that there was a "firefight" between rebels and NATO forces in Kandahar, but did not confirm whether air support had been called in.
President Karzai has previously cited civilian casualties caused by coalition forces' operations as "the main cause of strained relations between the United States and Afghanistan."
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