Suspected drug runners dressed in Mexican military-style uniforms who were involved in an armed confrontation with Texas lawmen were using a Mexican military-issue Humvee and weapons, the Hudspeth County sheriff said Friday.

"It was military," said Arvin West, whose officers were involved in the standoff. "Due to the pending congressional hearings I can't comment further."

West said the determination that the equipment was military-issue came from the federal government, but he wouldn't elaborate. A U.S. Army spokesman said he could not confirm West's statement, and the Mexican Foreign Relations Department said it would have no comment.

The Mexican government has denied that any soldiers were involved in the standoff that occurred Monday in a remote spot along the Rio Grande in West Texas. The smugglers escaped back across the border without a shot fired, abandoning more than a half-ton of marijuana as they fled.

Mexican officials have said the uniforms and other equipment could have been stolen.

Sen. John Cornyn, R-Texas, and other officials have said they will seek hearings investigating such border incursions.

U.S. Border Patrol Chief David Aguilar, in El Paso Friday, said he could not rule out Mexican soldiers' involvement in the standoff at Neely's Crossing, about 50 miles east of El Paso.

In Mexico, kidnappers and drug smugglers regularly wear police gear, which is sold at street stands.

On Thursday, Mexico's foreign relations secretary suggested the smugglers may have been U.S. soldiers or American criminals disguised as Mexican troops.

Aguilar said he has spoken with his Mexican counterparts and was assured that an intense investigation is under way in Mexico.

A California newspaper reported this month that Mexican military units had crossed into the United States 216 times since 1996. It cited a Department of Homeland Security document, but department Secretary Michael Chertoff has said many of those incidents were just mistakes.

Also Friday, Aguilar said Border Patrol and other law enforcement are reporting that a new violent tactic is being used against them: "flaming rocks," rocks wrapped in cloth, dipped in gasoline, set on fire and thrown across the border.

Most of the incidents have happened near San Diego, and one officer has been injured, he said.

Authorities fear a deadly confrontation as attacks against Border Patrol agents increase. Last fiscal year there were 778 reported incidents, compared with 396 in 2004.