The truth about UFO activity would be released to the public if David Cameron became prime minister.
David Cameron has vowed to publish any secret files that may exist on UFOs if he becomes prime minister.
Speaking at one of his regular Cameron Direct public meetings, he pledged to be "open and frank" with any government knowledge about close encounters.
The Conservative leader was responding to a question about apparent government cover-ups of UFO activity.
Mr Cameron joked: "I'm convinced we've been visited by aliens - one of them is trade secretary Peter Mandelson."
At the meeting in Tynemouth, North Tyneside, he was questioned about a spate of mysterious incidents.
A member of the audience asked: "In July last year the respected scientist and astronaut Dr Edgar Mitchell, who was the sixth man to walk on the moon, spoke on a British radio station.
"He said the American government had had contact with extra terrestrials on multiple occasions and that these were ongoing.
"He spoke about the Roswell event in 1947 where wreckage of a downed UFO was recovered and found to contain alien bodies.
"He said this event was real but was covered up by the government for many years.
"Do you agree with me that the British people have a right to know if we have been visited, and if so, when you become prime minister will you seek to lift the veil of secrecy and give the public the truth that they deserve?
Mr Cameron replied: "I have no idea there is intelligent life out there and no idea whether any of the sightings which have taken place or whether any incidents which have taken place have any basis in truth.
"When people have looked at the Roswell incident, or when people have looked at pictures... a rational explanation tends to be produced to try and show what has happened is not what those who believe in UFOs suggest.
"But I think we should be a open as possible, so I would be quite happy to give you a guarantee that if I became prime minister I would always be entirely open and frank about these things.
"I don't think any of us have any clue whether there's intelligent life out there and it is certainly not something that any government should seek to hide from anyone."