MEXICO CITY - The men dressed in military garb who crossed the border and confronted Texas law officers this week were drug smugglers, not Mexican soldiers, officials said Wednesday, illustrating Mexico's thorny problem with criminals who masquerade as security forces.

Photos of what appeared to be Mexican troops in U.S. territory during the incident Monday shocked many Americans, although Mexico quickly denied its military was involved. But to most Mexicans it just offered further proof that drug traffickers run rampant around the border area in military-style vehicles, wearing uniforms and, in some cases, using military firepower.

“It is known that these are drug traffickers using military uniforms and they were not even regulation military uniforms,” Mexican presidential spokesman Ruben Aguilar told reporters.

A U.S. law enforcement official said the FBI and other agencies found no evidence the uniformed men were Mexican soldiers. The official spoke on condition of anonymity because of the sensitivity of the matter.

Both countries said they were investigating the case, which comes at a time of rising anger over border security, with Washington considering extending a wall along its 2,000-mile-long frontier with Mexico - an idea Mexicans bitterly resent.

“We have communicated at the diplomatic level with the government of Mexico on the matter and requested that they investigate the matter - and that U.S. authorities are already investigating the incident,” State Department spokesman Sean McCormack said in Washington.

The Mexican government also cited its long-standing policy that its soldiers must stay away from the border unless they have special authorization.

In Mexico, kidnappers and drug smugglers regularly wear police gear. Caps, vests and T-shirts bearing official-looking logos for Mexico's federal police force are sold at street stands. Some police even rent out their uniforms or patrol cars to shakedown artists.

“It's very easy to go out and buy military uniforms in a store. ... It's very easy to get (uniforms) for any police agency you want to imitate,” said Rodolfo Casillas, a professor at the Latin American School for Social Sciences.

Rick Glancey of the Texas Border Sheriffs' Coalition said the faceoff began 50 miles east of El Paso when state police tried to stop three sport utility vehicles on Interstate 10. The vehicles made a quick U-turn and headed south toward the border, a few miles away.

Crossing the border, one SUV got stuck in the Rio Grande River, and men in a Humvee tried in vain to tow it out.

Then a group of men in civilian clothes began unloading what appeared to be bundles of marijuana, and torched the SUV before fleeing.

The Mexican army press office said it had no information on Monday's incident.

Mexico's Foreign Relations Department said in a statement that the confrontation, in which shots were not fired, could have been staged to “damage the image of our armed forces and bilateral cooperation.”

Recent reports that Mexican army and police have crossed into the United States about 20 times a year have irked border states - even though Homeland Security Secretary Michael Chertoff played down the problem, noting that in many places the border is not clearly marked.

Mexico has struggled to remove corrupt law enforcers and keep security equipment out of the wrong hands. But police and soldiers have been arrested and charged with carrying out drug operations and even kidnappings.

One of the most high-profile cases involves the “Zetas,” a gang of deserters from an elite Mexican army military unit that has fought a bloody turf war to control trafficking routes on the border.

Aguilar, the presidential spokesman, said fighting organized crime is “a long-term, short-term and medium-term battle that this administration faces, and that will also face the following administrations.”

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On the Net:

Mexican President Vicente Fox's English language Web site:

http://www.presidencia.gob.mx/en/