Newly obtained audio of a bizarre UFO incident that occurred in the skies above Arizona last month has been released online, providing first-hand evidence of a strange aerial encounter that nobody at the FAA has been able to explain.

The incident, which took place on the afternoon of February 24 in the airspace over southern Arizona, began when the pilot of a Learjet 36 airliner operated by Phoenix Air Group contacted Air Traffic Control, after witnessing something he couldn't comprehend.

"Was anybody above us that passed us, like, 30 seconds ago?" the pilot asks, stammering a little, which you can hear in recordings originally obtained from the FAA by The Drive, excerpts of which are posted below.

"Negative," the air traffic controller, stationed at Albuquerque's Air Traffic Centre in New Mexico, replies to the pilot.

"Okay…" the pilot confirms, sounding unconvinced. "Something did."

Another pilot on the recording says "A UFO!", and the first pilot simply replies, "Yeah."

After a few minutes pass, the air traffic controller contacts another airliner in the vicinity, an Airbus A321 operated by American Airlines, to tell them to keep a lookout for anything that passes over them in the next 15 miles.

"If anything passes over?" the pilot asks, sounding confused.

The air traffic controller explains the situation regarding the previous unexplained sighting, and the Learjet pilot clarifies things to the extent that he can, describing what he did – and didn't – see.

"I don't know what it was, it wasn't an airplane but it was… the path was going in the opposite direction."

Moments later, the Airbus pilot confirms that he too has witnessed whatever the strange object is.

"Yeah something just passed over us, like a… I don't know what it was, but it was at least 2,000–3000 feet above us. Yeah it passed right over the top of us."

The controller presses him as to whether the UFO was "in motion or if it was just hovering", but the Airbus pilot isn't totally sure.

"I couldn't make it out if it was a balloon or whatnot, but it was just really beaming light or had a big reflection and several thousand feet above us going the opposite direction."

When asked if it was a Google balloon, the Airbus simply responds, "Doubtful."

These exchanges, which are thought to have taken place over the span of just 6 minutes, are all that remain of a bizarre incident that doesn't appear to have ever been formally written up by aviation authorities, despite the seemingly invisible presence of a UFO detected by two separate aircraft in a highly trafficked airspace.

The only thing that seems to be for sure, is that the FAA looks like it has no idea what this strange airborne mystery was either – explaining that it wasn't aware of any unusual aircraft or weather balloon experiments in the area on the day that could account for what the pilots saw.

"We don't have any comment beyond what you hear," the FAA said in a statement issued to media outlets.

"Other than the brief conversation between two aircraft, the controller was unable to verify that any other aircraft was in the area. 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."

As The Drive points out, the region in which the sightings took place is nestled in the midst of numerous military and air force facilities, and is an area "known for being highly active with military aircraft, and even possibly clandestine aircraft that remain under a cloak of secrecy".

That's one explanation.

But a series of recently declassified Air Force videos suggests these unexplained encounters don't always originate inside the US military complex.

So where else could they come from? Nobody really knows.