Former American President Ronald Reagan asked Mikhail Gorbachev for help from Russia to 'fight the alien invader'.

The president and former actor went off-script during a peace summit in Geneva in the 1980s to ask the Soviet leader for his support in the event of an invasion from extra terrestrial life.

Reagan repeated the warning when he spoke to a group of students, and his subsequent speeches were examined by his advisers to remove any mention of aliens in them.

Ronald Reagan (right) met Mikhail Gorbachev (left) for the first time at a peace summit in Geneva, Switzerland in 1985 and asked for his support in the event of an alien invasion

The warning was revealed in a book about UFOs by Dr David Clarke, which examines the extent to which Americans believed in stories about aliens.

He suggests his words may show that Reagan, who was inspired by science fiction movies, saw there could have been a threat from aliens.

The President is believed to have become an avid science fiction fan while working in Hollywood as a B movie actor and was said to be addicted to films like The Day the Earth Stood Still and Close Encounters.

He confessed his favourite story was 'the invasion from outer space that prompts earthlings to put aside nationalistic quarrels and band together to fight the alien invader'.

Reagan even arranged a private screening of Stephen Spielberg's Close Encounters of the Third Kind at the Whitehouse in 1982 for top judges, astronauts and other VIPs.

In 1985 he went a step further and directly addressed Gorbachev at a summit to ask for his support in the event aliens were to invade.

Ronald Reagan asked Mikhail Gorbachev for support fighting a future alien invasion at a peace summit

'He surprised Gorby by saying he was sure the two superpowers would co-operate if Earth was threatened by alien invasion,' Dr Clarke said.

'Taken aback, the Soviet leader politely changed the subject.'

Reagan apparently then told his inner circle he felt he had 'scored a point' over his counterpart.

Deputy national security adviser Colin Powell was said to be horrified by the mention of aliens at the meeting. He then found Reagan repeated the story to a group of Maryland high school students after his return to the US in 1985.

Powell's solution was to go through the President's public speeches deleting 'interplanetary references' right until Reagan's final months in office.

Dr Clarke said that at any mention of an alien invasion Powell would roll his eyes and say 'Here come the Little Green Men again.'

The book suggests Reagan was secretly appalled by nuclear weapons and his approach to Gorbachev may have been inspired by the 1951 movie, The Day the Earth Stood Still.

In the film, an interplanetary peace-keeping force lands on earth using an invincible giant robot to force the warring nuclear powers to put aside their differences.

Dr Clarke said: 'For a generation that lived in fear of the bomb, this message of salvation from the stars, delivered by technological angels, was a welcome alternative to the Cold War stalemate.

'Ronald Reagan was a born-again Christian and saw no contradiction between his faith and a belief in aliens.'

Mikhail Gorbachev, pictured in Germany in November 2014, was said to be shocked by Reagan's request

Dr David Clarke, who wrote How UFOs Conquered The World, said Reagan appeared to believe in aliens

Dr Clarke said the President may also have been convinced he was speaking for the American public because of a poll released, shortly after Close Encounters hit film screens.

According to a Gallup poll, 57 per cent of Americans believed that UFOs were real, compared to 27 per cent of the British population. Seven per cent claimed to have actually seen one.

Dr Clarke added: 'Ronald Reagan is remembered for his warnings about the danger posed by the "evil empire" by which he meant the Soviet Union.

The former US President was said to be obsessed with science fiction films like Close Encounters

'But he was also obsessed with science fiction movies - in particular The Day the Earth Stood Still - and his comments to Gorbachev at the 1985 summit in Geneva imply that he might have believed the real threat came not from behind the Iron Curtain but from hostile extra-terrestrials.

'He wasn't the first world leader to suggest that the nations of the Earth would only unite in the face of a common foe from outer space.

'In 1947, just a couple of months before the Roswell incident, the British foreign secretary Anthony Eden - who was to become Prime Minister in 1955 - said he feared the world would only be united when we "find someone in Mars to get mad against."'