Academic experts on the radical right have raised “alarm” that the US could see a “rapid" rise in right-wing extremism and domestic terrorism following the 2020 presidential election.

In an open letter sent to The Independent, 17 specialists on radical right discourse warn that “anti-democratic methods will become normalised in pursuit of still darker, radical-right agendas.”

“We fear that should election violence or a contested outcome in the US come to pass, there could be a rapid increase in radical-right extremism, including increased risks of domestic terrorism,” the letter reads.

Donald Trump has on a number of occasions refused to commit to a peaceful transfer of power in the event he loses the 3 November presidential election to Democratic rival Joe Biden.

The scholars express fears that the president’s refusal to accept the result of the election in the event of a narrow margin will further encourage a radical-right agenda.

“As experts and practitioners on the radical right globally, past and present, we have seen this movie before,” the letter says.

If Mr Trump refuses to accept the election outcome and presents a host of legal challenges that delay the transfer of power, the country could be left in unprecedented territory. States such as New York have been actively preparing for violent demonstrations in the wake of the election.

"Every scholar on the radical right I know is raising the alarm around this election,” Professor Matthew Feldman, a specialist on Anglo-American right-wing extremism and a Professorial Fellow at the University of York told The Independent.

The document hosts signatures from a number of experts at respected institutions across the world including Dr Louie Dean Valencia-García, Texas State University; Prof Inderjeet Parmar, City, University of London; and Dr Eviane Leidig, Center for Research on Extremism, University of Oslo.

The letter states that under Mr Trump “radical right activities” including “alleged electoral interference, voter suppression and misinformation” and “repressive policing” have surfaced in the run-up to the election.

It also alleges that under his administration there has been a “deliberate rousing of radical-right militia and anti-governmental groups.”

Prof Feldman said experts’ concern comes both from Mr Trump’s leadership and the administration’s “whispering” of “sweet nothings” into the ears of white supremacists and other right-wing extremists such as the Proud Boys.

Mr Trump told the far-right group, which has embraced white nationalism and espoused fascist views, to “stand back and stand by” during the first presidential debate, rhetoric which some interpreted as a show of support.

“Too many of them - from the Proud Boys to the Oath Keepers to fascist groups like the American Identity Movement and an array of militants on the alt-right - are interpreting this administration’s statements as licence to disrupt or even attack the US elections,” the letter says.

The president has come under fire for his repeated reluctance to distance himself from conspiracy theorists and white supremacists.

“The dog-eat-dog amoral ruthlessness of Mr Trump’s divisive model of society underscores the threat to US representative democracy and a prelude to a dystopian era of harshness and repression in which ‘the land of the free and the brave’ becomes unrecognisable,” Dr Alan Waring, an independent scholar, author and original draftee of the letter, said.

Signatories say “public officials – from the highest in the land to police officers on the beat across the US – must remember their democratic obligations, and put these first.”

They conclude: "We thus appeal to all persons of goodwill to be positive and proactive in the defence of democracy. History may not simply repeat itself, but those of us professionally engaged in the study of the radical right can all too balefully recognise its distinctive voice."