The San Antonio Express-News reports Zapata County Sheriff Sigifredo Gonzalez Jr. said as many as 10 of the Mexican helicopters have been spotted flying over south Texas in daylight during the past 17 months.
U.S. Federal and state agencies would not elaborate on the missions, the newspaper said.
But a Mexican official with knowledge of the flights said, "Yes, I can tell you they exist, they are going on -- certainly for the last couple of years."
Most of the helicopters have been sighted near Falcon Lake, where Mexican authorities are battling the Zetas cartel, the Express-News said.
U.S. Rep. Michael McCaul, who represents part of Harris County and is chairman of the Homeland Security Oversight and Investigations Subcommittee, would not confirm details about the flights.
"It is a highly sensitive, coordinated effort to take out the cartels that has been effective," McCaul said. "Beyond that, I don't want to compromise the operations or the safety of our agents."
Catherine Frazier, deputy press secretary for Texas Gov. Rick Perry, said state law enforcement officials are not told in advance of the flights.
"Failure to do so stirs up unnecessary concern among local people and could result in situations of mistaken identity or friendly fire, putting our peace officers and citizens in harm's way," she said.
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