Mexican drug cartels are using improvised armored vehicles known as "monsters" to protect their narcotics shipments from rival gangs, a military officer who spoke on condition of anonymity told Efe.

The officer is assigned to the 8th Military Zone based in the northeastern border state of Tamaulipas, where troops have seized around 110 armored cars, including more than 20 monsters that evoke scenes from the 1979 film "Mad Max."

Most are heavy trucks that were equipped with armor at clandestine workshops, mostly located in Tamaulipas. Some of the vehicles can carry 12 gunmen, the officer said.

Soldiers dismantled one workshop in the Tamaulipas town of Camargo in a June 2011 operation, seizing two armored vehicles and nearly three-dozen more - including 23 tractor-trailers and other heavy trucks - that had not yet been plated.

One monster seized last year weighed more than 30 tons because it was covered in thick steel plates and further reinforced with railroad tracks.

The officer said troops also confiscated a cargo van dubbed the "pope-mobile" that had an elevated cabin similar to the "room" in the Roman Catholic pontiff's vehicle, although the Mexican van was secured with metal plating instead of bullet-proof glass.

"The vehicles are built with steel plates at least an inch thick. Small-caliber projectiles, such as bullets from assault rifles, have a hard time penetrating the armor. They can only be destroyed with heavy weapons or anti-tank shells," the officer added.

"They don't circulate on roads or in the cities, but instead operate on byways, which are the routes used to take drugs to the border with the United States," the source said.

The brutal turf war being waged in Tamaulipas between the Gulf and Los Zetas gangs - former allies turned arch-enemies - has forced both organizations to develop these armored vehicles to run their businesses.

The officer noted that the state has vast semi-arid plains with hundreds of small side roads and byways where the traffickers transport their drugs in light vehicles escorted by the monsters.

A ranch where suspected Zetas hit men killed 72 undocumented migrants in August 2010 - apparently after they had refused to work for the gang as enforcers or couriers - was located on one of these unpaved side roads in Tamaulipas.

"The cartels are fighting to control and protect these routes both for drug- and people-trafficking and in the opposite direction for the smuggling of weapons to Mexico, as well as to bring in a large quantity of merchandise illegally," the source said.

Founded by deserters from an elite special forces unit, Los Zetas began as the armed wing of the Gulf cartel, but ended that relationship in March 2010 to go into business for themselves.

Hundreds have died in the ensuing turf battles between the aggressive upstarts and the established drug trafficking organizations.

Mexico is mired in a wave of organized crime-related violence that left 47,515 dead between December 2006 - when President Felipe Calderón took office and militarized the struggle against the country's heavily armed, well-funded drug mobs - and Sept. 30, 2011, according to official figures.

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