Donald Trump appeared to endorse the "QAnon" conspiracy theory over the weekend after playing a piece of music associated with the movement at a campaign rally in Ohio.

During the same speech, members of the audience in Youngstown also raised their index fingers, a gesture closely associated with the conspiracy movement, which dates back to 2016.

The hand gestures at the rally and the choice of music intensified fears that Trump was indicating his support for the conspiracy theory movement described by the FBI in August 2019 as a growing domestic terrorist threat.

"QAnon figures are claiming the use of the song brings some kind of legitimacy for them," Alex Kaplan, a senior researcher for the US media watchdog Media Matters wrote on Twitter.

"Trump Sending a Clear Message Patriots," a QAnon-linked account on the pro-Trump social media network Truth Social wrote. "He Re-Truthed This for a Reason."

According to analysts at Media Matters, the piece played at the rally and on the videos was "Wwg1wga" – an acronym for the QAnon slogan "Where we go one, we go all."

A spokesman for Trump insisted the music was a Mirrors, composed by Will Van De Crommert, whose credits include writing music for the 2018 Summer Olympics in Rio de Janeiro. However, analysis by the website, using audio editing software found the two pieces were virtually identical.

QAnon centres on the belief that America is controlled by a secret elite cabal of Satan-worshipping child abductors headed by, among others, Hillary Clinton and George Soros.

It is based on theories floated by an alleged senior anonymous official, known as Q, who has "exposed" the workings of the "deep state" in postings on far-right websites. The country, QAnon believes, can only be saved by a true patriot, like Donald Trump.

It is not the first time Trump has flirted with imagery or music associated with QAnon. He has sent similar signals on his social media network Truth Social, using the same music in campaign videos as well as promoting a raft of conspiracy theories himself.

For instance, postings by the former president included a claim that a report would show the 2020 election was fraudulent and that he should be reinstalled in the White House.

There are now more than 300 QAnon-linked followers on Truth Social, where they have been welcomed after being banned by Twitter, YouTube and Facebook.

During the rally in Ohio, Trump doubled down on accusations that he was persecuted by the FBI and unfounded claims that the 2020 election was rigged.

"We are a nation that has weaponised its law enforcement against the opposing political party like never ever before," the former president said as his audience expressed approval.

"We have got a Federal Bureau of Investigation that won't allow bad election changing facts to be presented to the public," he added.

America also had "a Department of Justice that refuses to investigate egregious acts of voting irregularities and fraud," he continued. "We have a president who is cognitively impaired and in no condition to lead our country which may end up in World War Three.

According to one estimate, 8 per cent of Americans – around 22 million people – believe in QAnon.