Far-right extremists – particularly white supremacists – were responsible for more than half of the deaths attributed to extremists in the United States last year, according to a report issued this week by the Anti-Defamation League.

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Twenty of the 34 extremist-related killings in 2017 were carried out by far-right extremists, more than double the number that group was responsible for in 2016, according to the ADL’s annual report on extremist-related killings in America.

Eighteen of those 20 deaths were caused by white supremacists, according to the ADL.

The incidents noted by the ADL included the August 2017 death of Heather Heyer, 32, who was protesting a rally organized by white supremacists in Charlottesville, Virginia, when authorities said she was mowed down by a vehicle driven by James Alex Fields, 20.

“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,” ADL CEO Jonathan Greenblatt said in a news release.

The deadliest incident of last year, however, was carried out by an Islamic extremist. Eight people died in October when a man identified as Sayfullo Saipov, 29, plowed a pickup truck into bicyclists and pedestrians on a path in New York City.

Including the October killings, a total of nine deaths were attributed to Islamic extremists, according to the ADL. Black nationalists were responsible for five of the killings reported in 2017, according to the ADL.

“These findings are a stark reminder that domestic extremism is a serious threat to our safety and security,” Greenblatt said. “We saw two car-ramming attacks in the U.S. 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 ADL urged officials to “use their bully pulpit to speak out against racism, anti-Semitism and all forms of bigotry at every opportunity” to mitigate the extremist threat. The ADL also recommended that federal and state officials create programs to help those trying to leave extremist movements and to “thwart (the) recruitment of disaffected or alienated Americans.”

Read the full report from the ADL