A gruesome video depicting the decapitation of five members of a Mexican drug cartel by a rival gang has been posted on the Internet in the latest atrocity in the raging battle over drug-smuggling routes

The video shows masked members of the Gulf cartel standing behind five shirtless members of the Zetas cartel, who have black 'Zs' painted on their chests. The masked men are wielding machetes and slap their prisoners, who are kneeling below them, as they each state their name for the camera. When they are asked who sent them, they each reply "Z-40". 40 is the name given to Miguel Angel Treviño Morales, the Zeta cartel's second-in-command. The camera then shows three of the men start the grizzly, slow process of beheading them as they hack and saw at their necks with the machetes. When the process is over, after almost two painstaking minutes, the masked men hold the severed heads up like they are trophies. The video was shot in Río Bravo, Mexico, along the U.S. border. The Zetas were founded by former soldiers who defected from the Mexican military in 1998 to work as hired killers for drug traffickers. They have since carved out their own smuggling empire, expanded massively across Mexico and diversified into kidnapping, extortion and theft of crude oil.