Racially motivated extremists and militia extremists present the most lethal domestic terrorism threats in the United States, officials warn, and the threats could grow this year.
The revelations of the "elevated threat" are in an unclassified intelligence report released more than two months after a mob of insurrectionists stormed the US Capitol.
The blunt assessment echoes recent warnings made by US officials, including FBI director Christopher Wray, who testified this month that the threat from domestic violent extremism was "metastasising" across the country.
Attorney-General Merrick Garland has also described it as a top priority as his Justice Department works to prosecute hundreds of people who made their way into the Capitol as Congress was gathering on January 6 to certify Joe Biden's election victory.
The riot laid bare the threat posed by domestic extremists and led Biden, weeks later, to assign his intelligence officials the task of studying the scope of the problems.
A brief and unclassified summary of that threat assessment was made public on Wednesday. A full classified report was presented to the White House and Congress.
Intelligence officials say in their assessment that extremists seen as risks for violence are motivated by a range of ideologies.
Developments such as the anger over restrictions imposed during the coronavirus pandemic and a belief in the debunked narrative that November's presidential election was fraudulent "will almost certainly" spur additional violence in 2021, the report says.
Numerous courts and Donald Trump's own Justice Department upheld the integrity of the election.
The report says the most lethal threat is presented by racially motivated violent extremists, who officials say are most likely to conduct mass attacks against American civilians, and militia groups, who are seen as likely to target law enforcement and government officials.
The threat from militias increased in 2020 and is expected to increase again this year, the report's summary says, with the report saying white supremacists display "the most persistent and concerning transnational connections".