FBI file reveals 1983 plot to kill Queen Elizabeth II during US visit

A version of this story appeared in the May 26 edition of CNN's Royal News, a weekly dispatch bringing you the inside track on Britain's royal family. Sign up here.

Britain's Queen Elizabeth II faced a potential assassination threat 40 years ago, ahead of a trip to the United States, according to newly released documents from the Federal Bureau of Investigation.

A cache of 103 pages were posted to the FBI's online records site, The Vault, on Tuesday. The files cover preparations for several trips the late Queen made to the US, including an official tour of the West Coast with her husband, Prince Philip, in 1983.

One document appears to detail a tip gathered around a month before that visit from San Francisco police regarding a phone call from "a man who claimed that his daughter had been killed in Northern Ireland by a rubber bullet."

It continues: "This man additionally claimed that 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 same document notes that "it is the intention of the Secret Service to close the walkways on the Golden Gate Bridge when the yacht nears." There's no mention of any precautions that may have been taken at the national park nor do the files reveal whether any arrests were made.

The files illustrate the FBI's hypervigilance at possible threats to the visiting British monarch, collaboration with the US Secret Service and concerns about the Irish Republican Army (IRA) and its sympathizers during royal visits.