The U.S. Federal Aviation Administration took the extraordinary step of barring all flights to and from El Paso International Airport in Texas, which borders Mexico, for 10 days, citing “special security reasons,” the FAA said.

Airline sources told Reuters the grounding of flights was believed to be tied to the Pentagon’s use of counter-drone technology to address Mexican drug cartels’ use of drones along the U.S.-Mexico border.

The move has stranded numerous aircraft from Southwest Airlines and American Airlines at the airport.

The El Paso airport confirmed the development in a post on Instagram.

Nature of security reasons not specified

The FAA did not specify the nature of the “security reasons” and declined to comment beyond the notice. It said the temporary restrictions would be in place until February 21. It does not apply below 18,000 feet (5,486 meters), which allows airplanes to transit over the airspace.

In mid-January, the FAA warned airlines to exercise caution when flying over Mexico, Central America and parts of South America, citing the risks of potential military activities.

Tensions between the U.S. and regional leaders have ramped up since the Trump administration mounted a large-scale military buildup in the southern Caribbean, attacked Venezuela and seized its president, Nicolas Maduro, in a military operation.

Trump said in January that drug cartels were running Mexico and suggested that the U.S. could strike land targets to combat them, in one of a series of threats to deploy U.S. military force against cartels.