Two separate flights reported seeing the same 'UFO' in the Arizona desert in February.

Two airline pilots spotted a mysterious, reflective object hovering some 40,000 feet (12,000 meters) over southern Arizona last month, and the Federal Aviation Administration (FAA) is stumped.

According to radio transmissions between the befuddled pilots and air traffic controllers (which you can listen to in full, thanks to an FAA recording recently released to the Phoenix New Times), the sighting occurred around 3:30 p.m. local time on Feb. 24, somewhere over the Sonoran Desert near Phoenix.

"Was anybody above us that passed us like 30 seconds ago?" the first pilot asked while flying a Learjet west toward California. [7 Things Most Often Mistaken for UFOs]

"Negative," an air traffic controller at the FAA's Albuquerque Air Traffic Center in New Mexico answered.

"OK," the pilot responded. "Something did."

The object, whatever it was, was flying high — at least a few thousand feet above the jet, which was cruising at an altitude of around 37,000 feet (11,000 m), the New Times reported. A few minutes later, the FAA asked another nearby flight — an American Airlines Airbus traveling in the same direction — to keep an eye out for anything "passing over" it in the desert.

The confused pilot agreed. And sure enough, within a few minutes, the Airbus crew saw the same mystery object fly over their plane.

"Yeah, something just passed over us," the Airbus pilot reported. "I couldn't make it out, whether it was a balloon or what … but it had a big reflection on it and it was several thousand feet above us, going the opposite direction."

Several weeks later, authorities are still stumped as to the object's origin. Beyond these two pilot reports, the FAA couldn't verify that any other aircraft were around. It likely wasn't a "Google balloon," the FAA reported, nor a weather balloon or a military craft.

"We have a close working relationship with a number of other agencies and safely handle military aircraft and civilian aircraft of all types in that area every day, including high-altitude weather balloons," an FAA representative told the New Times.

In other words, whatever the UFO was, the FAA should have known about it. But it didn't.

This report comes just a few months after a former Pentagon official revealed that the government has been quietly running an official UFO detection program since 2007. An investigation into the program by The New York Times turned up striking footage taken by two Navy fighter pilots, who appear to encounter a mysterious glowing object midair.

Reports like these may be more common than you imagine. According to the National UFO Reporting Center — an online database of alleged UFO sightings in America — there have been nearly 650 UFO sightings reported so far in 2018. However, the website advises, "Many of the new reports have been submitted by individuals who elect to remain anonymous… we encourage visitors to our website to be discriminating in what they accept as accurate and reliable."

Originally published on Live Science.