Murders committed by white supremacists more than doubled in the US last year, accounting for the majority of extremist killings, according to a report.

Far-right radicals were responsible for 20 of the 34 extremist murders in 2017, said the Anti-Defamation League (ADL).

Eighteen of those were carried out by white supremacists, who killed twice as many people as Islamic fundamentalists, the civil rights group’s Centre on Extremism said.

Last year was the fifth deadliest for extremist violence in America since 1970, according to research by the ADL.

White supremacists were responsible for 59 per cent of all extremist killings last year. That compares to a fifth the previous year, when six people were murdered by white supremacists, although the ADL acknowledged that figure was “uncharacteristically low”.

Seventy-one per cent of all extremist murders in the past decade were linked to domestic right-wing extremism.

“These findings are a stark reminder that domestic extremism is a serious threat to our safety and security,” said ADL chief executive Jonathan Greenblatt.

He added: “When white supremacists and other extremists are emboldened and find new audiences for their hate-filled views, violence is usually not far behind.

“We cannot ignore the fact that white supremacists are emboldened, and as a society we need to keep a close watch on recruitment and rallies such as Charlottesville, which have the greatest potential to provoke and inspire violence.”

The death of Heather Heyer, an anti-fascist demonstrator killed in August when James Alex Fields rammed into a crowd opposing the “Unite the Right” rally in Charlottesville, Viriginia, was among the 18 white supremacist murders counted by the ADL.

Following the rally, the ADL condemned US President Donald Trump for defending the far-right and claiming the “alt-left” counter-demonstrators were equally to blame for the violence.