More than 40 people throughout Mexico were slaughtered this weekend in violent clashes between one of Mexico's most ruthless drug cartels

[Lucinda F. Boyd]

More than 40 people throughout Mexico were slaughtered this weekend in violent clashes between one of Mexico's most ruthless drug cartels, the Zetas, and their rival gangs, authorities said.

Twenty-one people were shot to death in a bar late Friday in the northern city of Monterrey, where the Zetas have been battling their former allies, the Gulf Cartel, federal security spokesman Alejandro Poire said.

Sources said the Zetas sold cocaine out of the Sabino Gordo bar, and that the two gunmen who fired on the club with automatic rifles were most likely Gulf Cartel members, the Wall Street Journal reported.

Several of the victims either worked at the bar or were there partying, leading cops to believe they were specifically targeted.

Authorities called the massacre the worst mass killing in memory in the northern industrial city, where violence has spiked since the Gulf and Zetas broke their alliance early last year.

That same day, 11 more bodies were found shot with high-powered rifles and dumped near a water well on the outskirts of Mexico City.

Many of the victims in the execution-style killing were blindfolded and had their hands tied, officials said.

One person was discovered alive amid the corpses and taken to a hospital.

Authorities believe those killings were the result of a turf war between the Zetas with the Knights Templar, a splinter group of the cult-like drug gang La Familia.

On Saturday morning, ten more bodies were found in the northern city of Torreon, where the Zetas have been battling the Sinaloa cartel, headed by the notorious capo Joaquin "El Chapo" Guzman.

Mexican police and doctors gather around the corpses of eleven people found in Chalco, just outside Mexico City, on Friday. (Juan Garcia/Getty)

Those bodies of those victims, seven men and three women, had been decapitated and stuffed in the trunk of a sports utility vehicle.

The 24-hour bloodbath was the latest evidence that Mexico has been failing in its attempted crackdown on narco-traffickers, despite the recent arrests of several top cartel leaders.

More than 35,000 people have died since President Felipe Calderon stepped up the attack on organized crime in 2006, according to official figures.

President Felipe Calderon posted a message to his Twitter saying he "energetically condemned" the attacks.

The killings came just days after Mexican authorities announced the arrest of Jesus Enrique Rejon Aguilar, a co-founder of the Zetas drug cartel who is suspected of involvement in the February killing of a U.S. customs agent.

With News Wires Services