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.
Also detailed in the group's report are the killings of a couple in Reston, Virginia, who were shot dead by their daughter's boyfriend after reportedly convincing her to leave him over his white supremacist views.
The report also cites Jeremy Christian, an alleged extremist accused of fatally stabbing two strangers in Portland, Oregon, when they intervened in his anti-Muslim rant.
"The white supremacist murders included several killings linked to the alt right as that movement expanded its operations in 2017 from the internet into the physical world—raising the likely possibility of more such violent acts in the future," the ADL's report warns.
The deadliest extremist attack of 2016, however, was linked to Islamic extremism. Sayfullo Saipov, the man accused of killing eight people with a truck in New York in November, is said to have had connections to Isis.
The ADL said five murders were also carried out by black nationalists.
"Combined with other violent acts by black nationalists in recent years, these murders suggest the possibility of an emerging problem," the report adds.
Mr Greenblatt said: “The bottom line is we cannot ignore one form of extremism over another. We must tackle them all.”
In May last year, Mr Trump quietly cut $10 million (£7.7m) funding to groups which fight right-wing extremism in the US.
Critics have blamed the billionaire Republican's rhetoric during the election campaign and since becoming President for the re-emergence of white supremacist groups.