WASHINGTON -- The number of U.S. mass killings linked to extremism over the past decade was at least three times higher than the total from any other 10-year period since the 1970s, .

The report, provided to The Associated Press ahead of its public release Thursday, also found that all extremist killings identified in 2022 were linked to right-wing extremism, with an especially high number linked to white supremacy. They include a racist mass shooting at a supermarket in Buffalo, New York, that left 10 Black shoppers dead and a mass shooting that killed five people at an LGBT nightclub in Colorado Springs, Colorado.

"It is not an exaggeration to say that we live in an age of extremist mass killings," the report from the group's Center on Extremism says.

Between two and seven domestic extremism-related mass killings occurred every decade from the 1970s to the 2000s, but in the 2010s that number skyrocketed to 21, the report found.

The trend has since continued with five domestic extremist mass killings in 2021 and 2022, as many as there were during the first decade of the new millennium.

The number of victims has risen as well. Between 2010 and 2020, 164 people died in ideological extremist-related mass killings, according to the report. That's much more than in any other decade except the 1990s, when the bombing of a federal building in Oklahoma City killed 168 people.

Extremist killings are those carried out by people with ties to extreme movements and ideologies.

Several factors combined to drive the numbers up between 2010 and 2020. There were shootings inspired by the rise of the Islamic State group as well as a handful targeting police officers after civilian shootings and others linked to the increasing promotion of violence by white supremacists, said Mark Pitcavage, a senior research fellow at the ADL's Center on Extremism.

The center tracks slayings linked to various forms of extremism in the United States and compiles them in an annual report. It tracked 25 extremism-related killings last year, a decrease from the 33 the year before.

Ninety-three percent of the killings in 2022 were committed with firearms. The report also noted that no police officers were killed by extremists last year, for the first time since 2011.

With the waning of the Islamic State group, the main threat in the near future will likely be white supremacist shooters, the report found. The increase in the number of mass killing attempts, meanwhile, is one of the most alarming trends in recent years, said Center on Extremism Vice President Oren Segal.

"We cannot stand idly by and accept this as the new norm," Segal said.