Image copyright Getty Images Image caption Supporters displaying QAnon posters appeared at Trump rallies last summer

A California school fundraiser has been cancelled after conspiracy theorists spread the claim it was the target of a terror attack by an ex-FBI chief.

An innocuous tweet by James Comey about his previous jobs was interpreted online as code for a "false flag" assault on the family gathering.

The Grass Valley Charter School in California said it decided to stop the event out of an "abundance of caution".

Authorities expressed concern that internet vigilantes might attend.

The bizarre claims were perpetuated by followers of the so-called QAnon conspiracy theory.

They believe that US President Donald Trump and justice department special counsel Robert Mueller have secretly joined forces to foil a "deep state" coup of the US government, plotted by paedophiliac politicians and Hollywood figures.

Mr Comey's tweet on 27 April shared his employment history as a part of the #FiveJobsIveHad Twitter trend.

Conspiracy theorists pored over the posting, noticing that the first letter of each job he listed spelled out "GVCSF".

Internet searches revealed this to be an acronym for the Grass Valley Charter School Foundation.

QAnon adherents also rearranged the letters in the hashtag used by Mr Comey - "#FiveJobsIveHad" - to spell "five jihads".

They concluded the tweet and its timing was part of a plot hatched by the former FBI director to stage a terrorist attack on the school in Grass Valley, California.

It was noted that the school was due to hold a festival fundraiser on 11 May.

Image copyright Getty Images Image caption Mr Comey and Mr Trump have had a contentious relationship since Mr Trump fired him in 2017

The Grass Valley school has been in contact with law enforcement over the situation all week, according to a statement from the school's foundation.

The school, local police and FBI offices all received calls from believers of the conspiracy theory warning them of the imagined plot.

While the sheriff's office "deemed this entire situation as unfounded" and said there was "zero threat", the school still decided to cancel the Blue Marble Jubilee family festival.

Grass Valley Police Sgt Brian Blakemore told the San Francisco Chronicle that the callers seemed reasonable, but that it was feared they might "show up to guard the place".

Image copyright Blue Marble Jubilee/Facebook Image caption The school describes its annual Blue Marble Jubilee fundraiser as a "festival for families"

Wendy Willoughby, president of the school foundation, said they were "devastated" by the impact of the wild claims.

"Not only is it disappointing that the cancellation of this event deprives the families of our school and community a day of fun and connection, but the Blue Marble Jubilee also serves as a fundraiser.

"We now find ourselves not only out the potential dollars raised at the event, but also the money already spent in preparation."

It is not the first time outlandish ideas spread online have resulted in frightening real-world consequences.

In 2016, internet trolls shared the debunked claim that a child sex trafficking ring linked to senior figures in the Democratic party was operating from the basement of a pizzeria in Washington DC.

It resulted in a North Carolina man deciding to "self-investigate" by showing up at the restaurant with a rifle and shooting the lock off a closet.