(CNN) Claims of a Soviet plot to assassinate President John F. Kennedy as early as 1962 -- which the CIA ultimately dismissed -- were included in a 1963 memo to a top US investigation official, this week's dump of declassified JFK assassination files reveals.

The memo to James Lee Rankin -- then-general counsel for the Warren Commission -- details a tip that the CIA had received in the immediate aftermath of the killing from "an individual who described himself as a Polish chauffeur for the Soviet Embassy (in Canberra, Australia)." The memo says that the individual "touched on the possibility that the Soviet government had financed the assassination of President Kennedy."

Crucially, the memo also notes "the receipt of a similar anonymous telephone call on 15 October, 1962" -- more than a year before the assassination -- by "a man believed to be the same person."

Richard Helms, then the CIA deputy director for plans and the author of the memo, wrote: "It appears that the caller, who professes to be the Polish chauffeur of a Soviet Embassy car in Canberra [Australia] first phoned in over a year ago, on 15 October 1962, repeat 1962. At that time, he told a story about five Soviet submarines carrying 400 to 500 Soviet soldiers on their way to Cuba. One purpose of this troop movement, he said, was to support the Governor of Mississippi. He added that there was a plot to pay one hundred thousand dollars to kill President Kennedy. Behind the plot, he said, were the 'Iron Curtain countries,' and 'communist men in England, Hong Kong, and probably other countries.'"

Helms continued, linking the 1962 call to the call received a year later.

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