The U.S. military said U.S. and Afghan troops killed four Afghan civilians, including two women, during an operation in eastern Afghanistan.
The U.S.-led coalition had earlier said militants were killed Wednesday during a raid in Khost province. But Afghan officials disputed the claim, saying civilians, including a baby, were killed.
After an investigation, the U.S.-led coalition confirmed those killed were not involved in militant activities.
The U.S. military said U.S. and Afghan troops were targeting an enemy location when a nearby local family opened fire to "defend their home against an unknown threat." Troops returned fire, killing the civilians.
In a statement, U.S. Brigadier General Michael Ryan expressed regret and sympathy and said the surviving family members will be compensated.
Civilian casualties are a sensitive issue in Afghanistan, where the United Nations estimates more than 2,000 civilians were killed last year during militant attacks and foreign military operations.
Meanwhile, a suicide bomber struck in southern Afghanistan, killing five people during an attack on a counter-narcotics police convoy in Helmand province.
A provincial official, Daud Ahmadi, said two police officers and three civilians were killed when the bomber struck the convoy in the town of Lashkar Gah. Authorities blamed Taliban militants, who use the region's illegal drug trade to fund their insurgency.
Some information for this report was provided by AP.