As VOA's Greg Flakus reports from the border in Hudspeth County, in far-west Texas, local officials are worried about the potential for violent clashes.
There has been tension along the US-Mexico border in recent weeks following alleged incursions by Mexican military units guarding illicit drug shipments.
Hudspeth County's Chief Deputy Sheriff Mike Doyal was among the lawmen who came to the scene of a border drug smuggling operation on January 23.
It happened here, on the Rio Grande River, which forms the boundary between Texas and Mexico. Chief Deputy Doyal says his men were held at bay on this side of the border by heavily armed men who appeared to be Mexican soldiers.
"There was a military-style Humvee on the Mexican side,” said the deputy sheriff. “One of my first officers on the scene said it had been on this side with two subjects in it, one in the back with a heavy machine gun and one in the front with an assault-type weapon."
One of the vehicles the U.S. lawmen had pursued to the border became stuck in the river near the Mexican bank. Armed men unloaded the suspected drug load from the vehicle and then set the vehicle on fire and left the scene.
U.S. Ambassador to Mexico Tony
Garza demanded an investigation of the alleged incursion, but Mexico's Foreign Minister, Luis Ernesto Derbez, denied any Mexican troops had been involved. He suggested drug traffickers had been posing as military men.
That response provided little comfort to U.S. law enforcement officials like Mike Doyal.
"We have always tried to enjoy a good, working cooperative relationship with Mexico and would like to see it continue, but ultimately when it comes to cleaning up what is on the south side of the Texas border, it is up to the Mexican government. We cannot do it for them," said Doyal.
The incident on the river in Hudspeth County drew fire from the group that calls itself The Minutemen, and other groups calling for stricter control of the border. They cited over 200 other cases in which armed men, sometimes dressed in military uniforms, crossed over the border. Some incidents involved violence or threats against U.S. law officers.
The increased violence concerns the U.S. Border Patrol. El Paso Sector spokesman Doug Mosier says agents face constant danger. "We have had agents shot, we have agents physically assaulted, we have had agents rocked (People on the Mexican side throw rocks at the agents) from time to time."
Mosier says efforts to tighten control of the border after the September 11, 2001 terrorist attacks have resulted in more criminal gang violence directed at agents on patrol.