FBI reveals it foiled a 1980s plot to kill Queen Elizabeth II that involved dropping an object off the Golden Gate Bridge onto her royal yacht

• Newly released FBI files reveal a foiled plot to kill Queen Elizabeth II in 1983 during a US visit.
• The files say a man planned to drop an object off the Golden Gate Bridge onto the royal yacht.

The Federal Bureau of Investigation has released previously classified documents that show it helped to foil a potential assassination attempt targeting Queen Elizabeth II during her visit to the US in the 1980s.

A 102-page cache of files, which were made available on the FBI's "The Vault," reveals how a police officer alerted federal agents about statements made by a man he had encountered at an Irish pub in San Francisco, California, on February 4, 1983.

According to the files, the officer told agents that a man had communicated that he was seeking revenge for his daughter, who had been killed in Northern Ireland "by a rubber bullet."

The pub in question was known for being frequented by sympathizers of the Irish Republican Party, the documents said.

Queen Elizabeth II and Prince Philip, whose uncle Lord Mountbatten was killed by an IRA bombing four years earlier, were due to visit California a month later.

The documents say that the man was going to "attempt to harm" Queen Elizabeth II by dropping an object off the Golden Gate Bridge onto the Royal Yacht Britannia as it sailed underneath.

Failing that, he planned to kill the British monarch during her visit to Yosemite National Park, the documents said.

In response to the threat, the US Secret Service responded by making plans to "close the walkways" on the Golden Gate Bridge when the Queen's boat neared, per the files.

It's unclear if any arrests were made in relation to the assassination threat. Insider contacted the FBI for comment but did not immediately receive a response.

Despite the heightened risks outlined in the documents, Queen Elizabeth II's 1983 visit to the United States proceeded without incident. But the files outline the risk she faced during subsequent visits to the country.

An internal FBI memo included in the cache said "the possibility of threats against the British Monarchy is ever-present from the Irish Republican Army (IRA)" ahead of the late Queen's 1989 visit to Kentucky.

The files became public after US media outlets made Freedom of Information Act requests, per BBC News.