The Mexican government confirmed Wednesday that it had authorized the use of U.S. drones to collect intelligence on several occasions, a new sign of the two countries’ intensifying cooperation against the drug cartels threatening Mexico.

The statement from Mexico’s presidential office said the drones had been requested for “specific occasions and events” and had been operated under the supervision of its government.

But until now, the flights were secret, apparently out of concern about a possible backlash in Mexico. Mexican politicians and the public have historically been highly sensitive to U.S. involvement in the country.

The use of the drones was first reported by the New York Times, which said the Pentagon began sending high-altitude, unarmed drones deep into Mexico last month.

The Mexican government statement did not specify which U.S. agency was running the drones, and presidential spokesman Alejandro Poire did not return a call for comment.

The U.S. government has flown drones on the American side of the border for years. American officials have publicly hinted that the United States shares information from those flights with Mexico. Those drones are operated by the Department of Homeland Security.

On Wednesday, asked about the latest disclosure, one senior U.S. official said: “It’s been a process of cooperation over time, and so some suggestion that this is 10 days old wouldn’t be accurate.” The official spoke on the condition of anonymity because of the sensitivity of the matter.

The Pentagon referred calls to the Mexican government.

The U.S. and Mexican governments have rapidly expanded their cooperation in recent years against cartels that have been waging a ferocious war for control of drug markets and routes in Mexico. More than 35,000 people have been killed since President Felipe Calderon launched a military offensive against the cartels in 2006.

Some Mexican opposition politicians lashed out at the government for the secret drone flights.

“There are constitutional regulations that have to do with Mexican airspace,” Rosario Green, a former foreign minister and a senator from the Institutional Revolutionary Party, told the newspaper Reforma. “If there is nothing to hide, why not debate it in Congress, which at the end of the day has a lot to do with maintaining our national sovereignty?”

The Mexican government statement said the U.S. drone assistance was particularly sought in operations in the border area. When the drones were operating in Mexico, “the establishment of the objectives, the information to collect, and the specific tasks to carry out have been under the control of Mexican authorities,” the statement said.

Poire said in an interview with Mexico’s Radio Formula that the intelligence gathered by the drones had contributed to the arrest of drug lords.

The Times story said a U.S. Homeland Security drone had helped Mexican authorities locate several suspects in the slaying last month of Jaime Zapata, a U.S. Immigration and Customs Enforcement agent.

Matthew Chandler, a Homeland Security spokesman, declined to comment, citing the ongoing investigation into Zapata’s slaying.