More than half of extremist-related murders in the US are carried out by white supremacists, according to hate crime watchdog the Anti-Defamation League (ADL).
In 2017, white nationalists killed 18 people in the US, according to ADL's new report.
Other far-right extremists killed two, Islamic militants killed nine and groups it described as left-wing - including anarchists and black nationalists - killed five.
While the total number of extremist-related killings is about half of those committed in 2016, the number carried out by white supremacists doubled.
"These findings are a stark reminder that domestic extremism is a serious threat to our safety and security," ADL chief executive Jonathan Greenblatt said.
"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."
White nationalism has been on the rise in the US, with many blaming US President Donald Trump's policies and public statements. Mr Trump sparked outrage when he blamed "both sides" for the violence in Charlottesville, and recently railed against "shithole" countries in Africa.
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"The 18 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 said in a statement.
2017's figures were driven up by the Pulse nightclub shooting in Orlando, in which an Islamic militant shot 49 people dead. The motive for 2017's deadliest shooting - November's massacre in Las Vegas - has yet to be determined.
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Prominent alt-right figurehead Richard Spencer and ex-KKK leader David Duke have publicly supported Mr Trump, who has spent much of his first year as President trying to block people from Muslim-majority countries from entering the US, citing security concerns.