On the day John F Kennedy died, the CIA was working to kill Fidel Castro with a poisoned pen.

Mr Kennedy was assassinated in Dallas in 1963, but Mr Castro survived a CIA plot to kill him with a lethal ballpoint pen. In the end, the Cuban leader outlasted his American rival by more than five decades.

The machinations against Cuba’s communist leader are revealed in a new batch of declassified documents relating to Mr Kennedy’s assassination. The National Archives has been steadily making thousands of documents available to the public, helping to illuminate both the government’s scramble to investigate the President’s death and the Cold War geopolitics playing out around them.

The poison pen plot is striking for its synchronicity. According to a recently released document, on 22 November 1963, a CIA officer in Paris passed a Cuban asset a pen rigged with a hypodermic syringe.

Half a world away, tragedy was engulfing America.

“The evidence indicates that the meeting was under way at the very moment President Kennedy was shot”, the document says.

The assassination of JFK – in pictures Show all 8 1 /8 The assassination of JFK – in pictures The assassination of JFK – in pictures President John F. Kennedy and his wife Jacqueline Kennedy ride with secret agents in an open car motorcade shortly before the assassination, 22 November 1963 Getty The assassination of JFK – in pictures President John F. Kennedy and his wife Jacqueline Kennedy prior to his assassination Keystone/Getty The assassination of JFK – in pictures Kennedy is struck by an assassin's bullet as he travels through Dallas in a motorcade In the car next to him is his wife Jacqueline and in the front seat is Texas governor John Connally Three Lions/Hulton Archive/Getty The assassination of JFK – in pictures The view from the sixth floor window of the Texas School Book Depository in Dallas, from which Lee Harvey Oswald is thought to have assassinated Kennedy. This photograph was taken approximately one hour after the assassination Hulton Archive/Getty The assassination of JFK – in pictures Lee Harvey Oswald during a press conference after his arrest in Dallas. Lee Harvey Oswald was killed by Jack Ruby on 24 November on the eve of Kennedy's burial AFP/Getty The assassination of JFK – in pictures Lyndon B. Johnson takes the oath of office as President of the United States on the day of Kennedy's assassination. Jackie Kennedy is stood next to Johnson Getty The assassination of JFK – in pictures Kennedy's funeral procession goes into Arlington Cemetery in Washington Newsmakers/Getty The assassination of JFK – in pictures Kennedy's casket sat in the East Room of the White House Newsmakers/Getty

But it is clear that the attempt, while eerie in its timing, is far from unique. The 1967 document laying it out, entitled “Report on Plots to Assassinate Fidel Castro”, shows killing Mr Castro was a recurring obsession for the American president.

“We cannot overemphasize the extent to which responsible Agency officers felt themselves subject to the Kennedy administration’s severe pressures to do something about Castro and his regime”, the report says.

Among the other plots described are an effort to have Mr Castro ingest poison pills, which were supplied to members of a gambling syndicate working on behalf of the CIA and then passed to a Cuban exile leader in Florida; gifting Mr Castro a poisoned skin-diving suit; and boobytrapping “an unusually spectacular sea shell” so it would explode when the Cuban leader lifted it.

What are the JFK files?

Some plans were hatched before the Bay of Pigs debacle, in which an American-backed invasion of Cuba was easily repelled in a humiliating setback for the Kennedy administration. Early ideas included poisoning the air of a radio studio Mr Castro used and having him smoke a contaminated cigar before a speech, which would make him disoriented and undermine his credibility as he made “a public spectacle of himself”.

He wasn’t the only world leader the CIA targeted. A previously released summary of “CIA Involvement in Plans to Assassinate World Leaders” revealed that Dominican leader Rafael Trujillo was also in the agency’s sights.

But documents underline the CIA’s intense focus on disrupting Cuba and undermining Mr Castro. Many of those efforts sought to foment a popular uprising that would topple the revolutionary leader.