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 it had launched an investigation into the shootings.

Three other youths, whose ages ranged from 13 to 15, were wounded in a shooting attack in Ciudad Juarez on a vehicle. State prosecutors said three adults in the vehicle were killed in that attack.

Also Thursday, gunmen killed the head of a state police agency that prosecutes car thieves in the western state of Jalisco.

The Jalisco attorney general's office said Jesus Quirarte Ruvalcaba and his wife, Maria Guadalupe Aldrete Rosales, were killed in the city of Zapopan, just north of the state capital of Guadalajara.

Quirarte, 51, and Aldrete, 49, were traveling in a state-owned Dodge Ram, apparently en route to their jobs, when gunmen fired on them.

Investigators found about a hundred 9-mm and 7.62-mm shell casings at the scene. Those types of bullets are fired by assault rifles and machine pistols favored by drug gangs.

Violence has spread in Jalisco recently as rival gangs battle for control. On Feb. 12, armed men attacked a Guadalajara nightclub, killing six people and wounding dozens more.

In the Pacific coast resort of Acapulco, where the Mexican Open tennis tournament is being played, police reported finding a man's hacked-up body in five plastic bags, in a low-income neighborhood far from where the tournament is being held.

Elsewhere in Acapulco, police said they detained a 16-year-old youth and a 20-year-old man with four assault rifles and five hand grenades, traveling in a stolen SUV.