Four boys were among those killed during a military operation in Shahi Khil village in a district south of Kabul on Friday, which triggered a rash of protests in the capital.
Authorities at the scene in Wardak province, a Taliban hotbed, said the fatalities occurred when army mortar bombs landed near a local mosque and so far five soldiers involved in the operation have been detained.
"(We) urge the government to ensure an independent, impartial and transparent investigation and that those responsible be held accountable," the United Nations Assistance Mission in Afghanistan said in a statement.
Civilians have increasingly borne the brunt of the fighting around Afghanistan as local forces struggle to contain the expanding Taliban insurgency.
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Civilian casualties in Afghanistan hit a record high in the first half of 2015, with nearly 5,000 people killed or wounded, according to the United Nations.
The conflict has taken a particularly heavy toll on women and children.
The Taliban are responsible for most of the casualties, but as the Wardak incident shows there has been a sharp jump in those caused by pro-government forces.
In an audio message released by the Taliban yesterday, a man purported to be leader Mullah Akhtar Mansour offered his condolences to the relatives of the civilians killed in Wardak.
The message strongly rejected reports that Mansour was killed or critically wounded in a firefight with his own commanders on Tuesday.
In addressing the Wardak killings, the Taliban apparently aimed to deflect any suggestion that the message was an old or unauthentic statement from Mansour.