The JFK files Donald Trump announced the release of contain thousands of documents related to the assassination of the late President stored in the national archives.

Mr Trump announced: “Subject to the receipt of further information, I will be allowing, as President, the long blocked and classified JFK files to be opened.”

Speculation mounted among his critics that Mr Trump might have readily agreed to release the files in order to distract from the ongoing investigation into his alleged ties with Russia – although their publication was required by law following the 1992 Kennedy Assassination Records Collection Act.

This law – prompted partly by the Oliver Stone movie JFK, required the files, which run to millions of pages, many of them contained in CIA and FBI documents, to be published by 26 October, exactly 25 years after it was passed.

Over the years, the national archives has released the bulk of the documents, although some of them remain partially redacted. However, one final batch remains unreleased, and only the President has the authority to extend the secrecy of the documents past the deadline if he believes national security could be compromised by their opening.

Mr Trump has not yet said whether the remaining files will be released with partial redactions or in their entirety.

Pressure had grown on the President from historians and journalists to authorise the release of the files – with reported counter-pressure from the CIA Director Mike Pompeo to extend the secrecy of the documents for another 25 years.

Political consultant Roger Stone, a confidante of Mr Trump’s, told Infowars conspiracy theorist Alex Jones he had spoken to the President to urge him to release them.

“I had the opportunity to make the case directly to the President of the United States by phone as to why I believe it is essential that he release the balance of the currently redacted and classified JFK assassination documents,” Mr Stone said.

“A very good White House source — not the President — told me that the Central Intelligence Agency, specifically CIA director Mike Pompeo, has been lobbying the President furiously not to release these documents. Why? Because I believe they show that Oswald was trained, nurtured and put in place by the Central Intelligence Agency.”

Mr Stone, who wrote a book about the conspiracy theory that President Lyndon B Johnson, Mr Kennedy’s Vice President, was involved in the assassination, said he had not been given any indication as to Mr Trump’s intentions after he made his case for the documents’ release.

“He did not tip off his current decision…but he was all ears. He took it all in…I think he’s going to do the right thing.”

In pictures: JFK anniversary Show all 9 1 /9 In pictures: JFK anniversary In pictures: JFK anniversary dallas-9.jpg A combination picture shows (L) U.S. President John F. Kennedy and First Lady Jacqueline Kennedy Onassis greeting supporters at Dallas Love Field in Dallas, Texas on November 22, 1963 and (R) the same scene showing a remodeled air traffic control tower at the site of the original photo at Dallas Love Field in Dallas, Texas Reuters In pictures: JFK anniversary dallas-8.jpg A combination picture shows (L) Bill and Gayle Newman, civilian eyewitnesses to the assassination of President John F. Kennedy, covering their children as CBS News photographers Tom Craven (C) and Tom Atkins (R) take pictures in Dealey Plaza after shots were fired at Kennedy on November 22, 1963, and (R) visitors to Dealey Plaza using a tablet computer to photograph the site where President John F. Kennedy was shot nearly 50 years earlier, in Dallas Texas Reuters In pictures: JFK anniversary dallas-7.jpg A combination picture shows (L) U.S. Secret Service agents and local police examining the presidential limousine as it sits parked at Parkland Memorial Hospital in Dallas, Texas. (R) the same parking area for ambulances outside the emergency room at Parkland Memorial Hospital in Dallas, Texas Reuters In pictures: JFK anniversary dallas-6.jpg A combination picture shows (L) an unidentified uniformed police officer pointing at a seat in the Texas Theatre in Dallas, Texas in 1963. George Quartz, the events coordinator for the Texas Theatre, poses for a photograph (R) at the same location where Lee Harvey Oswald was arrested in Dallas, Texas Reuters In pictures: JFK anniversary dallas-5.jpg A combination picture shows (L) a Dallas Police Department vehicle parked in the 400 block of 10th Street in the Oak Cliff neighborhood of Dallas, Texas. A current photo (R) shows the same spot today Reuters In pictures: JFK anniversary dallas-4.jpg A combination picture shows (L) flower arrangements and spectators lining the street along Elm Street during a reconstruction of the Dealey Plaza crime scene in Dallas, Texas in 1963 and (R) visitors to Dealey Plaza walking along Elm and Commerce Streets in Dallas, Texas Reuters In pictures: JFK anniversary dallas-3.jpg A combination picture shows (L) cars traveling on the road past The Texas School Book Depository in Dallas, Texas in Dealey Plaza in November 22, 1963 and (R) the Sixth Floor Museum at Dealey Plaza (L) Reuters In pictures: JFK anniversary dallas-2.jpg A combination picture (L) shows the former residence of Lee Harvey Oswald at 214 West Neely Street in the Oak Cliff neighborhood of Dallas, Texas and (R) the same site today Reuters In pictures: JFK anniversary dallas-1.jpg A combination picture shows (L) Lee Harvey Oswald "holding a rifle in one hand and Communist newspapers in the other" in the backyard of 214 W. Neely Street in 1963 in Dallas, Texas, and (R) the backyard of 214 West Neely Street in the Oak Cliff neighborhood of Dallas, Texas Reuters

Some Republican politicians had also pushed for the files to be released, including Representative Walter B Jones and Senator Charles E Grassley, who introduced resolutions asking Mr Trump to “reject any claims for the continued postponement.”

Mr Kennedy’s assassination on 22 November 1963 rocked the world and speculation overwhether the hit by Lee Harvey Oswald was authorised by another party has never gone away.

Mr Trump is no stranger to the conspiracy theories that have swirled ever since the shocking day when the popular President was gunned down while sitting next to his wife as they were driven through the streets of Dallas.

During the 2016 presidential campaign, Mr Trump made an unfounded claim that the father of Republican rival Senator Ted Cruz was associated with Oswald – a claim he has never reneged on or apologized for.

Experts who have studied the assassination in detail believe there are around 3,100 previously unreleased files containing tens of thousands of never-before-seen material, some of which pertain to Oswald’s six-day trip to Mexico City around two months before the assassination.

Oswald, who had been monitored by the CIA, was shot and killed by nightclub owner Jack Ruby on 24 November, just a month after the Kennedy assassination.

Some believe the papers might show the extent to which the CIA was aware of the relations between Oswald and the Cubans and Soviets.

“I’ve always considered the Mexico City trip the hidden chapter of the assassination. A lot of histories gloss right past this period,” said Philip Shenon, a former New York Times reporter and author of a book on the Warren Commission, the congressional body that investigated the assassination.

“Oswald was meeting with Soviet spies and Cuban spies, and the CIA and FBI had him under aggressive surveillance. Didn’t the FBI and CIA have plenty of evidence that he was a threat before the assassination? If they had acted on that evidence, maybe it wouldn’t have taken place.

“These agencies could be afraid that if the documents all get released, their incompetence and bungling could be exposed. They knew about the danger of Oswald, but didn’t alert Washington.”

Jefferson Morley, a former reporter who has written extensively about the Kennedy assassination papers, said the remaining documents might include files on senior CIA officers from the 1960s who probably knew details of the agency’s surveillance of Oswald in Mexico City.

Mr Morley told the Washington Post he was keen to read a never-before released transcript of testimony given by James Angleton, the CIA’s chief of counterintelligence from 1954 to 1975, before the Senate in September 1975 investigating abuses committed by the intelligence community.

The majority of historians who have studied the assassination do not believe the release of the documents will lead to any new bombshells or conclusive pieces of information on the assassination.

“There's going to be no smoking gun in there,” Gerald Posner, the author of Case Closed: Lee Harvey Oswald and the Assassination of JFK, told CNN. “But anybody who thinks this is going to turn the case on its head and suddenly show that there were three or four shooters at Dealey Plaza — it's not the case.”

“Oswald did it alone,” Mr Posner said. “But what the files are doing and why they're important to come out is they fill in the history of the case and show us how the FBI and CIA repeatedly hid the evidence.”

Mr Posner said conspiracy theories about the CIA and mob working together to assassinate a head of state are true - but the target was the late Cuban leader Fidel Castro, not Mr Kennedy - whose brother Bobby was also assassinated in 1968.

“They tried seven times and they couldn't even wound him...they couldn't get rid of Castro, but somehow these same guys who were an 'F' there pulled off the perfect crime in Dallas, and 54 years later we can find not a shred of evidence about it. I just don't buy it,” he said.

Ken Hughes, a researcher at the University of Virginia, told CNN the files could reveal more about US involvement in the attempts to assassinate Castro as well as the US-approved coup of South Vietnamese leader Ngô Đình Diệm in 1963.