A UFO which was recently spotted by hundreds of people over Arizona was in fact a NASA research balloon, say the space agency.
 
Many reported the UFO sighting after seeing the 'balloon-like' craft in the skies on Sunday.

But a spokesperson for NASA today dashed the hopes of the would-be UFO-spotters by telling them the 'balloon-like' craft was just that ... a balloon.

NASA, and the Columbia Scientific Balloon Facility claim it was a 4,000-pound balloon sent to measure the gamma ray emissions at high altitude - like the one pictured.

It is said to have taken off on Sunday morning in New Mexico and drifted over Arizona before coming down at 9pm on Monday evening.