The amount of murders committed by white supremacists in the US last year was double that of Islamic extremists, helping 2017 become the fifth deadliest year for extremist violence since 1970.

According to a report by the Anti-Defamation League (ADL), white supremacists were directly responsible for 18 of the 34 extremist-related murders in 2017, compared to nine linked to Islamic extremists.

The report added that unlike in 2016, which saw 49 people shot in Orlando's Pulse Nightclub by an Islamic terrorist, a majority of the 2017 murders were committed by right-wing extremists in a trend that has continued for most years.

The reports says over the last decade, a 71% of extremist murders were linked to domestic right-wing extremists, compared to 26% committed by Islamic extremists

Despite being responsible for more deaths, an Islamic extremists still committed the deadliest single event, the truck attack on a bike path in New York City that killed eight people.

Heather Heyer was also killed in vehicle attack allegedly by James Fields during a far-right rally in Charlottesville, Virginia in another high profile attack during 2017.

Elsewhere, the report noted 2017 was the second year in a row that black nationalists have murdered in the US, suggesting a possibility of an "emerging problem".

Jonathan A. Greenblatt, CEO of the ADL, said: "These findings are a stark reminder that domestic extremism is a serious threat to our safety and security.

"We saw two car-ramming attacks in the US last year- one from an Islamic terrorist and another from a white supremacist in Charlottesville—and the number of deaths attributed to white supremacists increased substantially.

"The bottom line is we cannot ignore one form of extremism over another. We must tackle them all."

The reports adds that many of the far-right murders are linked to the alt-right movement after it expanded its from the "internet into the physical world" in 2017 – raising the likely possibility of "more such violent acts in the future".

The report gave the example of white supremacist James Harris Jackson, who travelled to New York from Maryland to allegedly stab homeless African-American man, Timothy Caughman, with a sword.

Jackson later admitted the murder was a "practice run" for a planned attack in Times Square.

The report adds: "It is quite likely that the future will see yet more violent acts stemming from the ranks of the alt right and the alt lite as more of their adherents move their activities into the real world."

The report does not include 2017 mass shooting in Las Vegas in which 58 people were massacred, as the motive of the gunman remains unknown.

Charlottesville
Members of white nationalists clash a group of counter-protesters in Charlottesville, Virginia, U.S., August 12, 2017. REUTERS/Joshua Roberts

Elsewhere, five of the 34 murders (15%) in 2017 were committed by black nationalists. The worst case were the murders allegedly committed by Kori Ali Muhammad, who is accused of murdering a security guard at a hotel, before appearing to target white people in a shooting spree, killing three others.

Derick Lamont Brown, former Dallas chairman of the New Black Panther Party, shot and killed his godfather before opening fire on paramedics and a neighbour. He then took his own life.

The report adds: "Taken together, these incidents represent the most significant black nationalist-related violence since the early 1980s and should be something of a concern as a possible emerging extremist threat, though one that is so far still far smaller than threats posed by right-wing extremists and Islamic extremists."

University of Virginia march
White nationalists carry torches on the grounds of the University of Virginia on the eve of a planned Unite The Right rally in Charlottesville Reuters