President Donald Trump on Thursday ordered the unveiling of 2,800 documents related to the 1963 assassination of President John F. Kennedy but yielded to pressure from the FBI and CIA to block the release of some information to be reviewed further.

Congress had ordered in 1992 that all records relating to the investigation into Kennedy's death should be open to the public, and set a final deadline of Oct. 26, 2017, for the entire set to be made public.

Trump had confirmed on Saturday that he would allow for the opening of the documents, "subject to the receipt of further information."

Administration officials told reporters on a conference call that Trump ordered government agencies to study the redactions in withheld documents over the next 180 days to determine whether they needed to remain hidden from the public. After the review, Trump expected such withholdings to be rare.

The White House said remaining records with redactions would be released "on a rolling basis" in the coming weeks.

In a memo to government agency heads, Trump said the American people deserved as much access as possible to the records.

"Therefore, I am ordering today that the veil finally be lifted," he wrote, adding that he had no choice but to accept the requested redactions for now.

Trump added: "I hereby direct all agencies that have proposed postponement of full disclosure to review the information" and identify as much as possible what can be publicly disclosed without harming defence, intelligence, law enforcement and foreign policy operations.

CIA Director Mike Pompeo was a lead advocate in arguing to the White House for keeping some materials secret, one senior administration official said.

While Kennedy was killed over half a century ago, the document file included material from investigations from the 1970s and 1990s. Intelligence and law enforcement officials argued their release could put at risk some more recent “law enforcement equities” and other materials that still have relevance, the official said.

Trump was resistant but “acceded to it with deep insistence that this stuff is going to be reviewed and released in the next six months,” the official added.

QUELLING CONSPIRACY THEORIES?

Academics who have studied Kennedy's slaying on Nov. 22, 1963, during a motorcade in Dallas said they expected the final batch of files to offer no major new details on why Lee Harvey Oswald gunned down the Democratic president.

They also feared that the final batch of more than 5 million total pages on the Kennedy assassination held in the National Archives would do little to quell long-held conspiracy theories that the 46-year-old president's killing was organised by the Mafia, by Cuba, or a cabal of rogue agents.

Thousands of books, articles, TV shows and films have explored the idea that Kennedy's assassination was the result of an elaborate conspiracy. None have produced conclusive proof that Oswald, who was fatally shot two days after killing Kennedy, worked with anyone else, although they retain a powerful cultural currency.

"My students are really skeptical that Oswald was the lone assassin," said Patrick Maney, a professor of history at Boston College. "It's hard to get our minds around this, that someone like a loner, a loser, could on his own have murdered Kennedy and changed the course of world history. But that's where the evidence is."

Kennedy's assassination was the first in a string of politically motivated killings, including those of his brother Robert F. Kennedy and civil rights leader Martin Luther King Jr., that stunned the United States during the turbulent 1960s. He remains one of the most admired U.S. presidents.