A report released Wednesday said the number of slayings committed by white supremacists in the United States more than doubled in 2017 compared with the previous year.
The U.S.-based Anti-Defamation League noted in its report that while the U.S. death toll from extremism was down in 2017, it was still the fifth most violent year since 1970.
The report said several of the killings were linked to the alt-right movement, "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."
Thirty-four people were killed by domestic extremists in the United States in 2017, the ADL said, compared with 71 such killings in 2016 and 69 in 2015.
One of the most high-profile incidents of 2017 was the death of protester Heather Heyer in Charlottesville, Virginia, in August during a white supremacist rally, when a rally participant drove into a crowd of counterdemonstrators.
?Las Vegas shooting
Another major incident in 2017, the October 1 mass shooting in Las Vegas in which 58 people were killed during a country music concert, was not included in the study.
A spokesman for the ADL said, "There's no evidence that the Las Vegas shooter had any ideology at all. Nothing has come forth to suggest that he was an extremist or motivated by extremist ideas."
However, the report said that if new information emerged later that revealed an extremist killing, the annual totals would be revised to reflect that.
Wednesday's report also said 2017 was the second year in a row in which black nationalists committed killings in the United States, something the study authors also marked as an item of concern.
"Combined with other violent acts by black nationalists in recent years," the authors said, "these murders suggest the possibility of an emerging problem."
The report said firearms were the most popular weapon of choice in 2017 incidents, followed by vehicles and then by use of stabbing or cutting implements.
Vehicular homicides were mentioned as an item of particular concern, as they have become more common among terrorist attacks in Europe in recent years, and they could be increasing in the United States as well.
In fact, the deadliest U.S. extremist attack of 2017 was carried out with a rented pickup truck. On October 31, an Islamic extremist drove his vehicle onto a New York City bike path, killing eight people along a kilometer and a half of the path.
'Tackle them all'
ADL chief Jonathan A. Greenblatt noted that vehicular attacks were carried out last year both by a white supremacist and an Islamic extremist. "The bottom line is we cannot ignore one form of extremism over another," he said in a news release. "We must tackle them all."
The Anti-Defamation League, a civil rights organization that tracks anti-Semitism and abuses against other minorities, said 2017 was considered a less deadly year because there were no major incidents with high death tolls such as the Pulse nightclub shooting of 2016, in which 50 people were killed, including the shooter.
The report also noted that extremist killings that take place in prisons were "definitely" underrepresented because such incidents are less likely to be reported by prison officials or the media.
Two of last year's victims were corrections officers, and another was a police officer.
Additionally, study authors noted that death is not the only result of extremism. "It is important to note that the deaths described here represent merely the tip of a pyramid of extremist violence and crime in the United States," they said. "For each person actually killed by an extremist, many more are wounded or injured in attempted murders and assaults. ... Moreover, extremists engage in a wide variety of other crimes related to their causes, from threats and harassment to white-collar crime."