The infrared footage shows the plane soaring at high altitudes over Glen Rose, Texas, US on December 28.

Suddenly, another smaller craft appears above it.

The object speeds in the opposite direction before slowing down and disappearing.

Conspiracy theorist UFO Today posted the clip to his YouTube channel yesterday.

“When the airplane crosses the UFO the mysterious object disappears,” he explained.

“The camera tries to lock on the object after it disappeared, but it was just gone.

To read more and view the video, click here.