LONDON - The FBI uncovered a potential threat to kill Queen Elizabeth II during the 1980s while she was visiting the United States, files released online by the agency show.

The queen and her husband, Prince Philip, visited the United States from February to March 1983, at a time when Northern Ireland was experiencing a long period of sectarian violence known as the Troubles.

According to the 102-page document on the FBI's online vault, the threat came in a phone call from a man who claimed his daughter had been killed by a rubber bullet fired by British forces in Northern Ireland.

The man said he "was going to attempt to harm Queen Elizabeth" during her trip by dropping an object onto the royal yacht from San Francisco's Golden Gate Bridge or in an attack when she visited Yosemite National Park, the report said.

The intelligence came via a police officer who frequented a pub popular with sympathizers of the paramilitary Irish Republican Army (IRA), which opposed British rule in Northern Ireland, the report added.

The report also noted that the U.S. Secret Service was planning to close the Golden Gate Bridge's pedestrian walkway, but the document did not contain details of any arrests.

The files give an insight into the FBI's efforts to manage risks arising from the monarch's private and public visits to the United States from the 1970s onward, and they note that "several anonymous threatening telephone calls" about her were made to local police.

Many of the perceived threats the FBI assessed were related to the IRA, which killed the queen's cousin Louis Mountbatten with a bomb planted on his fishing boat in Ireland in 1979.

In another entry about Elizabeth's 1983 visit, police warned the FBI that "it will be very hard to anticipate and prevent incidents which may embarrass either the queen" or the then-president, Ronald Reagan.

In the end, her visit took place without any major incidents. Reagan hosted the queen at an official dinner where she toasted the United States' contribution to "the western alliance," and she in turn welcomed the Reagans on the Royal Yacht Britannia for their 31st wedding anniversary. Some of the queen's schedule was canceled because of heavy rain - prompting her to joke that the United States had caught British weather, The Washington Post reported at the time.

The FBI records reveal the agency's considerations about other protests planned for the queen's visits - including a Northern Irish group's plans to hold a soup line with free beer to protest the visit, demonstrations planned for when the queen attended a baseball game and an incident in which a pilot received a summons after flying a small plane trailing a banner bearing the words "England, get out of Ireland" over New York's Battery Park during the monarch's visit for the United States Bicentennial in 1976.

The FBI, which released the information in response to a Freedom of Information Act request from NBC News, said additional files may exist, although it did not specify when they might be released.

From the late 1960s until the Good Friday Agreement of 1998, violence between Irish nationalists and pro-British unionists in Northern Ireland claimed the lives of 3,600 people and wounded tens of thousands more.

The queen's death last year sparked mixed reactions in the Republic of Ireland, where the legacy of decades-long violence and colonialism are still felt.

In 2011, Elizabeth became the first British monarch to travel to the Republic of Ireland since its independence in 1922 - voicing her "sincere thoughts and deep sympathy" to "all those who have suffered as a consequence of our troubled past."

"With the benefit of historical hindsight, we can all see things which we would wish had been done differently or not at all," she said at the time, a year before she shared a historic handshake with a former commander of the IRA.