Mexico City, Mexico - Mexico's president said Wednesday that US drone flights were part of a collaboration that has existed for years between the two countries after US media reported increased cross-border aerial surveillance of drug cartels.

"There is nothing illegal and it is part of a collaboration and coordination," Claudia Sheinbaum said at her morning news conference.

"It is a coordination and collaboration protocol that has existed for years between the United States and Mexican governments," she added.

According to The New York Times, Washington has stepped up secret drone flights over Mexico in search of fentanyl labs as part of US President Donald Trump's campaign against drug cartels.

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The CIA has not been authorized to use the drones to take lethal action, and any information collected is passed to Mexican officials, the Times said, adding that the covert program began under Trump's predecessor, Joe Biden, but had not been previously disclosed.

Last week, Mexico's government said US military aircraft may have spied on drug cartels during recent flights near Mexican territory.

Mexico was aware of two such US military flights in late January and early February that were in international airspace, Defense Minister Ricardo Trevilla said.