The US government has observed “aircraft” with capabilities that no country on Earth is capable of, former Pentagon Military intelligence Official Luis Elizondo said.
Mr Elizondo said: “My personal belief is that there is very compelling evidence that we may not be alone.”
The former Pentagon official ran the Advanced Aviation Threat Identification Program which was created to identify possible security issues posed by the UFOs.
Revealing the evidence he had observed he said: “These aircraft – we’ll call them aircraft – are displaying characteristics that are not currently within the US inventory nor in any foreign inventory that we are aware of.
“Things that don’t have any obvious flight services, any obvious forms of propulsion, and manoeuvring in ways that include extreme manoeuvrability beyond, I would submit, the healthy G-forces of a human or anything biological.”
The expert has revealed he resigned from the Pentagon in protest over the secrecy surrounding the programme.
The $22million budget for the UFO investigation programme has proved “almost impossible to find” by investigators.
Explaining his opposition to the coverup of revelations the craft did not appear to originate from our planet he said people should be told the truth.
Mr Elizondo said: “That fact is not something any government or institution should classify in order to keep secret from the people.”
The mission statement of the organisation is to uncover the threat posed by the mystery craft “seemingly defying the laws of aerodynamics” through eyewitness accounts and data from technical instruments.
He said: “We found a lot.”
The programme has been faced with calls to have its funding slashed.
Ryan Alexander of Taxpayers for Common Sense said: ”It’s definitely crazy to spend $22 million to research UFOs.
“Pilots are always going to see things that they can’t identify, and we should probably look into them.
“But to identify them as UFOs, to target UFOs to research – that is not the priority we have as a national security matter right now.”
The news follows revelations that the US Navy tracked mysterious UFOs for two weeks before a bizarre encounter with one of the objects.
The US Government-funded programme investigated reports of UFOs between 2007 and 2012, including the mysterious Nimitz case of November 2004.
Now one of the navy pilots involved in the Nimitz case has spoken about what happened.
Cmdr David Fravor and Lt Cmdr Jim Slaight were two pilots each in an F/A-18F super hornet on a routine training mission 100 miles out over the Pacific Ocean off the coast of San Diego when it happened.
Mr Fravor, from Windham, New Hampshire, said they were asked by radio from the USS Princeton navy cruiser if they were carrying weapons, but the planes only had two dummy missiles.
The radio operator then told them: “Well, we’ve got a real-world vector for you.”