It is believed to be the first time the set of six 1963 original prints, taken from film by an amateur cameraman, Abraham Zapruder, have appeared at an international auction.

Zapruder, an interior designer who enjoyed making amateur films, was one of thousands who gathered in Dallas on 22 November 1963 to watch the presidential motorcade as the Kennedys travelled through the city in an opentop limousine.

Standing at Elm Street with his 8mm film camera on telephoto, Zapruder captured the moment Lee Harvey Oswald fired into the president's car. His 26 seconds of footage was the only clear film from the crowd to show Kennedy being shot.

It provided vital evidence in the official inquiry into the assassination and became iconic after the images were published by Lifemagazine.

The film, which was converted into stills by the Associated Press agency and distributed to the press at the time, includes an image of Jackie Kennedy climbing into the back seat of the presidential limousine in a desperate attempt to avoid the gunfire. Only a few originals survive to this day. The set is expected to reach up to �7,000 when it goes on sale in London on 13 November.

Yuka Yamaji, head of photographs at Christie's in London, said their significance could not be overestimated.

"AP's prints of Abraham Zapruder's footage chillingly captures those fatal moments of one of the most important moments in 20th century history, " she said. In the following decade, the grainy pictures became fixed in the world's consciousness, with artists such as Andy Warhol and Richard Hamilton using the images as reference points.

Zapruder's film was bought immediately after the assassination by Life, but was never released in its full form by the magazine. In 1975, Life returned the film to the Zapruder family, five years after his death. The only copies that officially exist were made for the Secret Service and the FBI.

In his lifetime, Zapruder spoke about capturing the assassination on film, saying that initially he thought the president was "pretending" to be hit when the car emerged.

He also spoke about a recurring nightmare, sparked by his experience, in which the film played out in his head until the fatal head shot snapped him awake: "The thing would come every night , , I wake up and see this."