Gunmen opened fire on six children playing in the yard of a home in the border city of Ciudad Juarez, killing three girls aged 12, 14 and 15, prosecutors said Thursday.
Three other children in the yard were not hit by the bullets in the Wednesday attack. Some were as young as 8.
Ciudad Juarez, in northern Chihuahua state across the border from El Paso, Texas, has been the scene of bloody drug cartel turf battles that have killed more than 6,000 people the past two years. In several instances, youths have been killed just because they were in the same home as the gunmen's intended targets.
The Chihuahua state prosecutors' office said in a statement that the gunmen in the Wednesday attack were apparently targeting the father of two of the dead girls in a dispute that may have involved low-level drug dealing.
Two of the dead girls were sisters, and the third victim was their friend.
Mexico's human rights commission said Thursday it had launched an investigation into the shootings.