A mysterious white plane spotted circling the Denver metro area on Wednesday has residents and authorities perplexed as no one can seem to identify where it came from or what it was doing.

The enigmatic aircraft appeared on flight trackers under the name 'IRON99' and came to Denver from California by way of the Rocky Mountains.

Once it arrived over the city, the plane inexplicably began circling the area, much to the confusion and consternation of those who saw it.

Ultimately, the aircraft left the area and flew towards Oklahoma City where it seemingly disappeared from the flight trackers.

Attempts to discern the nature of the plane have only added to the mystery as numerous agencies denied any knowledge of the aircraft or its maneuvers.

Amazingly, one Air Force Base said that the flight flew through their airspace but never checked in with the site and even NORAD told reporters that they were unaware of the plane as well.

The prevailing theory is that the aircraft was taking part in some kind of classified mission, of sorts, since it appeared to be performing military maneuvers and had been in contact with the US Army.

Should that be the case, it is still rather puzzling that the ostensibly clandestine flight was seen so openly by thousands of Denver residents.

Although it is likely that the mystery plane has a prosaic explanation, we can't help but note the irony of it appearing over the Denver area, since the city's airport is a fixture in conspiracy theory lore.

With that in mind, unless the story behind the unexplained plane is revealed, it's likely to be chalked up to yet another layer of intrigue surrounding the region already rife with rumors.

Coast Insiders looking to learn more about the tales that surround Denver International Airport can check out filmmaker Jay Weidner's 6/11/2007 appearance on the program.

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Source: ABC Denver