Suspected drug hitmen burst onto a ranch in northern Mexico and opened fire on a family gathering, killing five people.
Elsewhere, officials said three decapitated bodies were found in an empty lot on the eastern outskirts of Tijuana.
The gunmen fired on the ranch near the rural town of Aldama in Chihuahua state on Monday night, shooting the men, including two brothers and an elderly man, in the head, the state attorney general's office said on Tuesday.
Ranging in age from 18 to 67, the victims were riddled with more than 50 bullets in what appeared to be a gangland-style execution.
The shooting was believed to be part of a drug feud as gangs fight over smuggling routes into the United States.
Drug hitmen killed 13 people including a baby at a family party in the tourist town of Creel in Chihuahua state this month.
Prayer session targeted
In another attack on a drug rehabilitation center in Chihuahua's border city of Ciudad Juarez, hooded gunmen killed eight patients during a prayer session.
More than 2,300 people have died this year in Mexico's drug war, mostly between rival gangs, in a fight for control of smuggling corridors into California, Arizona and Texas.
Drug violence is intensifying and gangs are ever more brazen despite the deployment of 25,000 troops and federal police across Mexico by President Felipe Calderon.
Mexico's most-wanted man, Joaquin "Shorty" Guzman, is fighting local drug baron Vicente Carrillo Fuentes, boss of the Juarez cartel, for control of Chihuahua state and its smuggling routes.
Meanwhile, officials said the bodies found in Tijuana had messages written on their backs in permanent marker saying they worked for "the weakened 'engineer,'" a nickname for Francisco Sanchez Arellano, a top lieutenant in the powerful Arellano Felix drug cartel.
The killings were apparently carried out by a rival group.
Witnesses said the bodies were left near a trash heap and had their hands tied behind their backs. The heads were found nearby, and had been burned.
Baja California state prosecutor Rommel Moreno Manjarrez told the newspaper La Frontera that the murders likely resulted from a power struggle within the Arellano Felix cartel following the arrest last week of one of operation's key gunmen at a Tijuana casino.
Mexican cartels have turned to decapitating their victims as a way to intimidate their rivals.
Another decapitated body and a man who had been stabbed to death were found Monday on the outskirts of Tijuana.