A recently released Federal Bureau of Investigation (FBI) document has showed that late British monarch Queen Elizabeth II faced a possible assassination threat during her 1983 visit to the United States.

The revelation was made after the FBI released a cache of files relating to the Queen’s travels to the US after her death in September last year.

The document showed that the US authorities braced from threats of Irish Republican Army (IRA) during the late Queen’s visit.

The assassination threat was made to a police officer in San Francisco, who drank regularly at an Irish pub, BBC reported.

The report said that the American officer warned federal agents about a man who he knew through the pub sought revenge for his daughter who “had been killed in Northern Ireland by a rubber bullet”.

The threat was made on February 4, 1983, a month ahead of Queen Elizabeth II and her husband Prince Philip’s visit to California.

The plot involved attempting to drop ‘an object’ from the Golden Gate Bridge as the royal yacht Britannia sailed beneath it.

“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 document stated.

The Secret Service planned to ‘close the walkaways on the Golden Gate Bridge as the yacht nears’. However, it is unclear what measures were taken, but the visit went ahead and there were no arrests.

The 102-page document was uploaded to the FBI’s information website on Monday following a Freedom of Information Act request submitted by US media outlets.

There were also warnings of an attack by IRA sympathisers during a visit in 1981, the report added.

The late Queen’s state visits to the US, including the 1983 visit, came during heightened tensions amid the tensions in Northern Ireland.

The report further said that an internal FBI memo from 1989 read that “the possibility of threats against the British Monarchy is ever-present from the Irish Republican Army (IRA)”.

Elizabeth’s second cousin Lord Mountbatten was killed after explosives were detonated on his boat by IRA in the Republic of Ireland in 1979.