MEXICO CITY- Mexico's foreign secretary suggested Thursday that uniformed men using a military-style Humvee to help drug traffickers on the border could have been U.S. soldiers disguised as Mexican troops.
The comments by Luis Ernesto Derbez came a day after U.S. Ambassador Tony Garza issued a strongly worded statement asking the Mexican government to "fully investigate" Monday's border incident.
Derbez called Garza's comments out of line and said his office is sending a diplomatic note asking the ambassador to tone down his rhetoric.
The U.S. Embassy in Mexico made no immediate comment.
Derbez also said that men photographed by Texas law enforcement officers as they helped marijuana traffickers flee to Mexico on Monday could have been Americans, but he offered no evidence.
He appeared to refer to a case in which three U.S. soldiers have pleaded guilty to running a cocaine smuggling ring from a U.S. base in Colombia. A fourth is being tried in Texas this week.
"Members of the U.S. Army have helped protect people who were processing and transporting drugs," Derbez told a news conference. "And just as that has happened ... it is very probable that something like that could have happened, that in reality they (the uniformed men at the border) were members of some of their groups disguised as Mexican soldiers with Humvees."
Texas law enforcement officials originally said Mexican soldiers were involved in Monday's incident.
Mexican officials earlier have said the uniformed men were drug traffickers disguised as Mexican soldiers. Derbez said Thursday there was no proof that they were even Mexicans.
"There is a supposition here that this involved Mexican citizens, and that is absolutely incorrect," Derbez said. "There would have to have been racial descriptions, and that would imply a certain element of racial discrimination on the part of the American sheriffs."
Derbez said his diplomatic note to U.S. Secretary of State Condoleezza Rice would demand that U.S. officials tone down their comments on Mexico's security and immigration problems, and would request quick results of an investigation into the December shooting of a Mexican migrant.
He complained that Garza should have made his complaints through diplomatic channels.
"We should not convert this, as (Garza) apparently did by publishing his article, into a public relations issue," Derbez said, adding that Garza's comments were "not only wrong, but also don't correspond to reality."
A series of earlier spats have raised tensions between the two nations that largely disagree on the best way to thwart illegal immigration and drug smuggling along the 2,000-mile (3,200-kilometer) border.
Derbez said Mexico's official position on immigration is now to push not just for legalization and temporary work permits for Mexicans, but for migrants from Central America and other countries as well.
"In any immigration reform, there should be a clause that allows the regularization of all citizens ... not just Mexicans, but other nationalities," Derbez said.
The U.S. Congress has refused to approve any amnesty. Instead it is considering the possibility of extending walls along the border - an idea that Mexico bitterly opposes.
Monday's confrontation began 50 miles (80 kilometers) east of El Paso, Texas, 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 river, and the men with the 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 set the SUV on fire before fleeing.