The Arellano Felix drug trafficking organization in Mexico has hired foreign mercenaries, including at least one American who served in the U.S. Army Special Forces and one Lebanese, to train cartel security forces in advanced military tactics and surveillance techniques, senior law enforcement officials say.

The mercenaries are "helping to acquire weapons in the United States, and working in surveillance and counter-intelligence, how to operate in cells, how to use night-vision equipment, and combat strategy," said James Milford, deputy director of the U.S. Drug Enforcement Administration (DEA). "The decision to hire mercenaries is a conscious effort to arm, equip and train their people."

The result, according to the officials, is increased sophistication in the drug traffickers' ability to monitor and track law enforcement activities, as well as to protect cartel leaders and attack their enemies. The Arellano Felix organization is widely viewed as the most violent of the Mexican organizations, given to torture and murder.

Rep. Silvestre Reyes (D-Tex.), who publicized the presence of former U.S. soldiers working for Mexican drug-trafficking organizations in August, said the mercenaries' skills, coupled with the cartels' almost unlimited resources, led to "an unholy but willing marriage."

Reyes, who worked for 26 years in the Border Patrol before being elected, said the mercenaries offer "the full gamut of services, from use of explosives to weapons training to hand-to-hand combat, to even interrogation techniques."

The equipment provided by the mercenaries includes not just heavy weapons such as 50mm machine guns and rocket-propelled grenades, but night-vision equipment, encryption devices and equipment to intercept police communications.

"They are at a level of sophistication we have not seen before," Milford said. "What they are doing is extremely sophisticated, not something that was just learned in a classroom. It has been drilled into them. They have sophisticated electronic capabilities that are driving us crazy."

Milford said U.S. intelligence had detected at least one training camp run by mercenaries working for the Arellano Felix organization, in a mountainous area in that organization's territory near Tijuana.

Last year, the sources said, a Lebanese mercenary was killed in a shootout in Guadalajara while protecting Javier Arellano Felix. Correspondent Molly Moore in Mexico City contributed to this report.