By Patrick Rucker
MEXICO CITY (Reuters) - U.S. drones are conducting surveillance flights in Mexico as the two nations step up joint efforts to combat drug traffickers, the Mexican government said on Wednesday.
Use of the pilotless aircraft to scout drug gangs have yielded valuable intelligence, Mexico said, but the program may raise hackles about outside interference in a country mindful of its national sovereignty.
"These missions have been especially useful in helping combat crime and have increased the technological superiority of Mexican authorities," President Felipe Calderon's security council said in a statement.
The Pentagon began flying the unmanned missions over Mexico last month, and they have already uncovered information useful to officials investigating the killing of a U.S. customs agent, The New York Times reported.
U.S. authorities responded with outrage when Immigration and Customs Enforcement agent Jaime Zapata was shot on a highway north of Mexico City on February 15 in an attack by suspected drug gang members that also wounded his partner.
Responding to the drones report, the U.S. Department of Homeland Security (DHS) said it worked with Mexican authorities on a wide variety of law enforcement missions and declined to comment on the investigation into Zapata's killing.
"All U.S. cooperation with Mexico is at the government of Mexico's invitation and is fully coordinated with the government of Mexico," said DHS spokesman Matthew Chandler.
The Times said President Barack Obama and Calderon agreed that the drone missions should continue when the two men met in Washington this month.
Mindful of constitutional strictures and sensitivity over national sovereignty, Mexican officials are wary about accepting foreign personnel to help fight drug traffickers.
More than 36,000 people have been killed in drug-related violence since Calderon launched his military campaign against the drug cartels after he took office in late 2006.
Smugglers use Mexico as a transit point for cocaine from South America but local gangs also smuggle home-grown marijuana and have expanded into racketeering and other crimes.
Washington has promised Mexico $1.3 billion over several years in anti-drug equipment, such as Black Hawk helicopters, and training via the so-called Merida Initiative.
Several arms of U.S. law enforcement have a presence in Mexico and work with their counterparts to thwart the gangs.
(Additional reporting by Jeremy Pelofsky in Washington; Editing by Xavier Briand)