The US Federal Aviation Administration lifted emergency flight restrictions that had barred all flights to and from Texas' El Paso International Airport, which borders Mexico, after warning flights could be cancelled for 10 days, citing special security reasons.
The action barring flights at a single US airport appears unprecedented, government officials said. After the September 11, 2001 attacks, the FAA barred all civilian flights across the United States for several days.
A US official told Reuters Mexican cartel drones breached US airspace. The Pentagon took action to disable the drones and then the FAA and Pentagon determined there was no threat to commercial travel.
Airline sources earlier told Reuters the grounding of flights was believed to be tied to the Pentagon's use of counterdrone technology to address Mexican drug cartels' use of drones on the US-Mexico border.
The flight prohibition also covered some rural air space in neighbouring New Mexico.
Some airline sources also said the closure had been due to coordination issues between the Pentagon and FAA.
The move had stranded numerous aircraft from Southwest Airlines, United Airlines and American Airlines at the airport.
El Paso airport handles about 4 million passengers yearly. It confirmed the development in an Instagram post.
The FAA did not specify the nature of the "security reasons" and declined to comment beyond the notice.
It had said the temporary restrictions would be in place until February 21. It does not apply below 18,000 feet (5,486 metres), which allows airplanes to transit over the airspace.
Airlines were caught off-guard by the announcement, which occurred early Wednesday.
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.
That caution was lifted last week after Trump said the United States wanted flights to resume to Venezuela.
Tensions between the US 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 US could strike land targets to combat them, in one of a series of threats to deploy US military force against cartels.
After the attack on Venezuela, the FAA curbed flights throughout the Caribbean, forcing the cancellation of hundreds of flights by major airlines.
In December, a JetBlue passenger jet bound for New York took evasive action to avoid a mid-air collision with a US Air Force tanker plane near Venezuela, which did not have its transponder activated.
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