The calls were made by a Canberra-based informant who, claiming high-level contacts within Russia's "diplomatic establishment", went on to spill his guts about a Soviet Union plot to kill the President.

A flurry of cables between Canberra and Washington followed the tip-off, culminating in a clear missive from the highest echelons of the CIA: "If he calls again, do everything to identify him."

The calls were detailed in a series of intelligence memos declassified and released in a dump of almost 3000 documents related to the killing of President Kennedy on November 22, 1963.

Although the calls were quickly dismissed as "cranks", they sparked a CIA investigation that uncovered three years of correspondence between American officials and the mysterious Canberra figure referred to only as the "Polish driver".

CIA officials believed the Polish driver's contact with the United States Embassy in Australia began three years before President Kennedy's assassination with an intriguing call to Ambassador William J. Sebald.

"At 2055 hours on 9 August 1960 the marine guard telephoned Ambassador Sebald to say that he had a man on the chancery line who refused to give his name but wished to speak," read one cable sent from Canberra to the CIA's director in 1963.

"When the ambassador took the call the man said that he was, 'from across the Kingston Hotel'.

"He then said clearly that, 'The two men you are looking for are in Moscow'."

The "Kingston Hotel" was read by the Americans as a coded reference to the nearby Soviet Embassy.

South Canberra was a hotbed of Soviet activity during the cold war, and ASIO agents were known to keep a close eye on the embassy from a post in the Kingston Hotel.

The "two men" mentioned by the Polish driver were likely William Martin and Bernon Mitchell, code breakers from America's National Security Agency who had recently fled the United States.

One month after the Polish driver's prescient tip, Martin and Mitchell appeared at a press conference in Moscow to announce their defection to the Soviet Union.

"He went on to say that his boss, Kurdiukov, was having secret conferences in Moscow," the cable continued.

"Ambassador Sebald asked for the caller's name, but the caller replied: 'I have not been here long and I do not wish to work longer in this place'."

William Sebald was the United States Ambassador to Australia from 1957 to 1961, while Ivan Kurdiukov was a senior Soviet diplomat stationed in Canberra between 1959 and 1968.

Kurdiukov would later become embroiled in a separate scandal, when one of his embassy staff was exposed as an alleged Soviet spy in a sting by Australian authorities.

American intelligence officers believed the Polish driver rang the embassy again on October 15 1962, although records do not indicate what was discussed.

The same man was believed to have called a third time on November 23 1963, this time to speak about President Kennedy's assassination.

"Series of anonymous telephone calls to the office of the Naval Attache in Canberra, Australia, by a man claiming to have knowledge about a Soviet plot to assassinate President Kennedy," read one cable copied to the FBI, the White House and the Secret Service.

The CIA director's office responded to the calls six days later in a message copied to American bureaus in Canberra and Melbourne.

"Agree anonymous caller looks like a crank but please continue to follow-up," the cable read.

"If he calls again, do everything to identify him."

It appears from the cables that American authorities were never able to trace the so-called Polish driver nor verify any of his information.

"[Redacted] has no record of a Polish driver connected with Russian diplomatic establishment in Australia. They are all Russian," read handwritten notes on one report.

In May 1964 the Canberra calls were the subject of a memo sent from Richard Helms, a senior CIA officer who would go on to lead the agency, to J. Lee Rankin, the former Solicitor General of the United States.

Although the subject of the 1964 memo was listed in the CIA files, its contents have not been not disclosed.

Mr Rankin was at the time serving as the general counsel for the Warren Commission, a body set-up in 1963 to investigate the death of President Kennedy.

The commission concluded in September 1964 that Lee Harvey Oswald had assassinated President Kennedy and had acted alone in doing so.

Two days after he killed the President, Harvey Oswald was himself shot and killed on live TV by Jack Ruby, a nightclub owner from Dallas.

The JFK Assassination Records are a trove of documents released by the United States National Archives on July and October this year.

The killing of President Kennedy has been fertile ground for conspiracy theories, with the CIA, the KGB and the mafia variously put forward as culprits.

Although it will take some time for historians to comb through the complete set of documents, the release has already prompted a number of fascinating revelations.

One document from November 1963 stated that Harvey Oswald had met with an agent from the KGB's "assassination department" in Mexico City two months before the shooting.

Another file detailed concerns that Harvey Oswald was himself an agent of the KGB.

President Donald Trump has promised to release the small number of documents that have been withheld from release, despite initial attempts by security agencies to keep some records secret.