efe-epaCiudad Juarez, Mexico

Armed men entered a residence in this northern Mexican city on Friday and murdered 11 people, authorities said.

The massacre took place near a prison on the outskirts of Ciudad Juarez, which lies just across the Mexico-US border from El Paso, Texas.

The assailants tied up and tortured the eight men and three women before shooting them, official sources told EFE.

The Chihuahua state Attorney General's Office announced it was launching an investigation.

On Thursday, inmates at Aquiles Serdan prison in Chihuahua city, the state capital, fatally shot a prisoner reputed to be gang leader.

Eight other people were wounded in the incident.

Ciudad Juarez, where more than 3,100 people were slain in 2010 at the height of a battle for control between drug cartels, had 534 homicides in the first six months of this year.