Drug smuggling gangs in Mexico have sent well-armed assassins, or "sicarios," into Arizona to locate and kill bandits who are ambushing and stealing loads of cocaine, marijuana and heroin headed to buyers in the United States, the Department of Homeland Security has warned Arizona law enforcement authorities.

In a memo sent in May and widely circulated since, the department said: "We just received information from a proven credible confidential source who reported that a meeting was held in Puerto Penasco in which every smuggling organization who utilizes the Vekol Valley was told to attend. This included rival groups within the Guzman cartel."

Joaquín Archivaldo Guzman Loera heads what formally is known as the Sinaloa Cartel, which smuggles multi-ton loads of cocaine from Colombia through Mexico to the United States. One of the most powerful and dangerous drug gangs in Mexico, it also is known as the Guzman cartel, which has been tied to the production, smuggling and distribution of Mexican marijuana and heroin and has established transshipment outlets in the United States.

The Vekol Valley is a widely-traveled drug smuggling corridor running across Interstate 8 between the Arizona towns of Casa Grande and Gila Bend, continuing north towards Phoenix. It gives drug smugglers the option of shipping their goods to California or to major cities both north and east.

The Homeland Security memo said a group of "15, very well equipped and armed sicarios complete with bullet proof vests" had been sent into the valley. It said the assassins would be disguised as "groups of 'simulated backpackers' carrying empty boxes covered with burlap into the Vekol Valley to draw out the bandits." Once identified, the memo said, "the sicarios will take out the bandits."

The federal government has posted signs along Interstate 8 in the Vekol Valley warning travelers the area is unsafe because of drug and alien smugglers, and the local sheriff says Mexican drug cartels now control some parts of the state.

The signs were posted by the Bureau of Land Management (BLM) along a 60-mile stretch of Interstate 8 between Casa Grande and Gila Bend, a major east-west corridor linking Tucson and Phoenix with San Diego. They warn travelers they are entering an "active drug and human smuggling area" and may encounter "armed criminals and smuggling vehicles traveling at high rates of speed."

Pinal County Sheriff Paul Babeu, whose county lies at the center of major drug and alien smuggling routes to Phoenix and cities east and west, told The Washington Times earlier this month that Mexican drug cartels have posted scouts on the high points in the mountains and in the hills and "they literally control movement.

"They have radios, they have optics, they have night-vision goggles as good as anything law enforcement has," he said. "This is going on here in Arizona. This is 70 to 80 miles from the border -- 30 miles from the fifth-largest city in the United States."

The sheriff said he had asked the Obama administration for 3,000 National Guard soldiers to patrol the border, but instead got 15 signs. He also has confirmed that he got the Homeland Security memo warning of the assassins.

Rising violence along the border has coincided with a crackdown in Mexico on warring drug gangs, who are seeking control of smuggling routes into the United States. Mexican President Felipe Calderon has waged a bloody campaign against powerful cartels, and more than 28,000 people have died since he launched his crackdown in late 2006.

Rep. Lamar Smith of Texas, the ranking Republican on the House Judiciary Committee and a member of the House Committee on Homeland Security, has called the signs "an insult to the citizens of border states."

"American citizens should not have to be fearful for their lives on U.S. soil," he said. "If the federal government would do its job of enforcing immigration laws, we could better secure the border and better protect the citizens of border states."

Two years ago, U.S. Immigration and Customs Enforcement (ICE), the investigative arm of Homeland Security, said in a report that border gangs were becoming increasingly ruthless and had begun targeting not only rivals, but federal, state and local police. ICE said the violence had risen dramatically as part of "an unprecedented surge."

The Justice Department's National Drug Intelligence Center, in its 2010 drug threat assessment report, called the cartels "the single greatest drug trafficking threat to the United States." It said Mexican gangs had established operations in every area of the United States and were expanding into rural and suburban areas.