From a deadly ambush on a Pittsburgh synagogue that killed 11 to a Parkland, Florida school shooting that left 17 dead, every US "extremism-related murder" in 2018 was linked to the far right, according to a new report by the Anti-Defamation League (ADL).

Last year marked the most killings by far-right attackers since 1995, with 42 of 50 murders carried out with firearms, an annual report published by the ADL concluded.

The report adds that 2018 was the fourth-deadliest year on record since the ADL started tracking such murders in 1970.

"The white supremacist attack in Pittsburgh should serve as a wake-up call to everyone about the deadly consequences of hateful rhetoric," said Jonathan Greenblatt, the ADL's CEO, in a statement.

"It's time for our nation's leaders to appropriately recognise the severity of the threat and to devote the necessary resources to address the scourge of right-wing extremism."

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The ADL partly attributes the comparably high number of deaths to a series of mass shootings, including 17 incidents involving "shooting sprees that caused 38 deaths and injured 33 people".

One of the perpetrators, 17-year-old Corey Johnson of Florida, had switched from white supremacism and "allegedly converted to Islam" prior to stabbing several people during a sleepover, killing a 13-year-old and injuring two others.

Unlike previous years, the ADL included a new category of political motivation known as the incel (or "involuntary celibacy") movement.

The incel movement is a predominantly white online subculture populated by men who blame women for their failure to find sexual or romantic partners.

In November 2018, Scott Paul Beierle opened fire on a yoga studio in Tallahassee, Florida, killing 61-year-old Nancy Van Vessem and 21-year-old Maura Binkley. Four others were injured; Beierle killed himself.

Media reports later found that Beierle had posted several YouTube videos in which "he revealed deep-seated hatred towards women, particularly women in interracial relationships who had ostensibly betrayed their 'blood'", the report says.

Hate crimes on the rise

In California's Orange County on January 2, 2018, Samuel Woodward, a member of the neo-Nazi group Atomwaffen Division, stabbed to death Blaze Bernstein, a former classmate of Woodward's who was gay and Jewish. Woodward was charged with first-degree murder with hate crime enhancement.

In February 2018, Nikolas Cruz shot up his former high school in Parkland, Florida, killing 17 and wounding 17 more.

In October 2018, white nationalist Robert Bowers allegedly stormed a Pittsburgh, Pennsylvania synagogue and shot dead 11 worshipers. Authorities charged him with 44 counts, including religious hate crimes.

The youngest victim was 53 years old and the oldest was 97.

Barry Werber, a 76-year-old survivor of that attack, later told the Associated Press, "I don't know why he thinks the Jews are responsible for all the ills in the world, but he's not the first and he won't be the last."

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Werber added, "Unfortunately, that's our burden to bear. It breaks my heart."

In the wake of the massacre, critics accused US President Donald Trump of stoking hatred and inciting against minorities, a charged Trump rejected.

Writing on Twitter after visiting the community in the wake of the incident, Trump dismissed the criticism and claimed his office was "shown great respect on a very sad and solemn day" in Pittsburgh.

The FBI reported a 17-percent rise in hate crimes in 2017, the largest increase in more than a decade.