The report by the Anti-Defamation League
, which monitors domestic extremism, shows white supremacist groups are going beyond spreading their doctrine online
and are taking it into the real world. It also finds extremist movements are not just relying on guns but using vehicles as weapons to commit attacks in the United States.
Last year, extremists of all types killed at least 34 people in the country, with some of those deaths making national headlines, according to the report.
The Las Vegas shooting, which left 58 people dead
in October, is not included in last year's tally because the killer's motive remains unknown.
But even without that number, 2017 was the fifth-deadliest year for extremist violence since 1970, the report said.
"Extremism in any form is an issue (whether it's) foreign born, politically minded extremism or racially focused extremism," said Jonathan Greenblatt, CEO of the Anti-Defamation League.
Of the total number of people killed by domestic extremists last year, right-wing extremists were responsible for 20 deaths, with 18 of those by white supremacists alone, the league said.
One high-profile killing was the August death
of Heather Heyer in Charlottesville, Virginia, who died after a car plowed into a crowd of people protesting a white supremacist rally.
"Heyer's death received national attention
and for many served as a wake-up call to the dangers posed by a re-energized white supremacist movement," the league said.
Last year's deaths by domestic extremists also includes nine by Islamic extremists and five by what the league described as black nationalists.
The vehicular attack on a New York bike path that left eight people dead was considered the single deadliest Islamic extremist attack last year.
"The deadliest extremist-related incident in 2017 involved a vehicle. Given the murder of Heather Heyer also involved a vehicle, the most highly publicized Islamic extremist and white supremacist-related murders in 2017 each used vehicles as weapons -- a first for the United States," the league said.
The ninth death as a result of a suspected Islamist extremist attack was the February killing of a transit security guard in Denver, allegedly by a man who had converted to Islam, according to the report.
The five deaths attributed to black nationalists included a man accused of fatally shooting three white men in April
At least 71 people died in extremist-related killings in 2016, according to the league. The majority of those were from the Orlando nightclub shooting
that left 49 people dead and was blamed on an Islamic extremist.
Also in 2016, two alleged black nationalists killed eight police officers in Dallas
and Baton Rouge, Louisiana,
the league said.
In 2015, there were 69 deaths blamed on extremists, the league said, numbers that include the San Bernardino, California, mass shootings by an Islamic extremist. The Bureau of Alcohol, Tobacco, Firearms and Explosives told CNN one of the guns used in the shooting was legally purchased.
The deadliest year for domestic extremist killings was in 1995 when 184 people were killed, the group said. The figure included the 168 people who died in the Oklahoma City bombing that April.