A former Pentagon official, who led the recently revealed multi-million dollar secret US programme to investigate unidentified flying objects (UFO), believes that there is evidence of alien life reaching Earth.

Luis Elizondo, who resigned from the Department of Defence in October, told CNN that we are not alone and there is a possibility that alien aircraft visited Earth.

"My personal belief is that there is very compelling evidence that we may not be alone," Elizondo told CNN on Monday.

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This bombshell information comes out after The New York Times reported over the weekend reported that the Advanced Aviation Threat Identification Program was started in 2007 with an annual funding of $22 million to find alien life. Senator Harry Reid of Nevada started the programme, which ended in 2012, because he believed that the extraterritorial life exists.

Elizondo resigned from his post because of the excessive secrecy surrounding the programme. He said that there is evidence that "stopped him from ruling out the possibility that alien aircraft visited Earth."

"These aircraft are displaying characteristics that are not currently in the US inventory nor in any foreign inventory that we are aware of," Elizondo told CNN.

"The programme sought to identify what had been seen, either through tools or witness reports, and then ascertain and determine if that information is a potential threat to national security. We found a lot," he added.

He revealed that they recognized "anomalous" aircraft that were "seemingly defying the laws of aerodynamics."

"Things that don't have any obvious flight services, any obvious forms of propulsion, and manoeuvering in ways that include extreme manoeuvrability beyond, I would submit, the healthy G-forces of a human or anything biological."

The New York Times report had a pair of videos that shows pilots capturing a fleet of a mysterious object going against the strong wind.

David Fravor, a retired commander and one of the pilots, told CNN that in 2004 he witnessed an object that resembled like a "40-foot-long Tic Tac" and changing its direction rapidly during a flight.