Newly released Federal Bureau of Investigation (FBI) documents have revealed an alleged plot to assassinate the late Queen Elizabeth II while she was a visit to the US in 1983, the media reported on Friday.
On Monday, the FBI released a 102-page cache of files, which was uploaded on the agency's information website Vault, relating to the late British monarch's travels to the US, following her death last year, reports the BBC.
The documents were published after a Freedom of Information Act request submitted by American media outlets.
The assassination threat was made to a police officer in San Francisco, the files reveal.
Aan officer who frequented an Irish pub in San Francisco warned federal agents about a call from a man he had met at the venue.
The officer said the man told him he was seeking revenge for his daughter who "had been killed in Northern Ireland by a rubber bullet".
The alleged threat came on February 4, 1983 -- about a month ahead of Queen Elizabeth II and her husband Prince Philip's visit to California.
"He was going to attempt to harm Queen Elizabeth and would do this either by dropping some object off the Golden Gate Bridge onto the Royal Yacht Britannia when it sails underneath, or would attempt to kill Queen Elizabeth when she visited Yosemite National Park," the BBC quoted the document as saying.
In response to the threat, the Secret Service had planned to "close the walkways on the Golden Gate Bridge as the yacht nears".
It is unclear what measures were taken at Yosemite, but the visit went ahead. No details of arrests were published by the FBI.
Many of the late Queen's state visits to the US came during heightened tensions amid the Troubles in Northern Ireland.
In 1976, the late Queen was in New York City for America's Bicentennial celebrations.
The documents reveal how a summons was issued to a pilot for flying a small plane over Battery Park with a sign that read "England, Get out of Ireland".
The late monarch's second cousin Lord Mountbatten was killed in an Irish Republican Army (IRA) bombing off the coast of County Sligo, Republic of Ireland, in 1979.
Ahead of a personal visit by the late Queen to Kentucky in 1989, an internal FBI memo read "the possibility of threats against the British Monarchy is ever-present from the IRA".
It continued that "Boston and New York are requested to remain alert for any threats against Queen Elizabeth II on the part of IRA members and immediately furnish same to Louisville," in Kentucky, the BBC reported.
On a state visit in 1991, the late Queen was scheduled to see a Baltimore Orioles baseball game with then President George H. Bush.
The FBI warned the Secret Service that "Irish groups" were planning protests at the stadium and "an Irish group had reserved a large block of grandstand tickets" to the game.
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