WASHINGTON - Amid the ongoing U.S. protests over the death in police custody of George Floyd, state officials have blamed outside extremist agitators, saying they mix with legitimate protesters to foment violence.

Minnesota Governor Tim Walz cited unconfirmed reports Saturday that white supremacists had been behind violent protests in Minneapolis where Floyd, who was African American, died last Monday.

When that assertion was not borne out, President Donald Trump pointed a finger at extremists of a different hue: left-wing anti-fascist activists known as antifa.

Blaming antifa for violence that took place at protests around the country, Trump vowed to designate it as a terrorist organization.

Attorney General William Barr, for his part, warned that violence committed by antifa and other similar groups is "domestic terrorism" and will be treated as such.

Here is a look at the extremist movements suspected of involvement in the protests:

White supremacists

White supremacists are individuals and groups that believe in the supremacy of the white race, oppose immigration and, in some cases, advocate the expulsion from the country of non-whites. Once boasting organized groups such as the Ku Klux Klan and neo-Nazi organizations, the movement has become increasingly disjointed and leaderless in recent years, with most members now operating online.

Although many white supremacists don't advocate violence, a growing number of individuals inspired by far-right ideology have carried out deadly shootings in recent years. The violent elements of the far right are known as "accelerationists" because they seek to accelerate a race war. FBI Director Christopher Wray has said that most of the FBI's domestic terrorism investigations involve white supremacist groups.

Boogaloo Boys

A relatively new incarnation of the anti-government militia movement, the Boogaloo Boys are an online community of pro-gun activists who advocate for a second boogaloo, their term of choice for civil war. The movement took off last summer when white supremacists appropriated the term for a cause of their own: a race war as opposed to a civil war, according to Megan Squire, a professor of computer science at Elon University. Mostly, though not exclusively, white, Boogaloos have been promoting themselves as libertarians fighting tyranny, according to Squire.

Antifa

Depending on whom you ask, antifa, short for anti-fascist, is a movement of far-left activists opposed to neo-Nazis and other extremist groups or, as one critic put it, an "extreme anarchist-communist movement."

Organizing on social media, antifa followers show up at right-wing rallies dressed in black and wearing masks and often engage in violent confrontations.

Antifa sympathizers were among counter-protesters at the 2017 "Unite the Right" rally in Charlottesville, Virginia, that turned violent.

The Southern Poverty Law Center says it does not label antifa as a hate group in part because antifa members "do not promote hatred based on race, religion, ethnicity, sexual orientation or gender identity."

Given that antifa is not a group, it is uncertain how Trump intends to label it as a terrorist organization. A Justice Department spokeswoman did not respond to a request for comment.

Anarchists

With sympathizers on both the right and the left, anarchists see government as illegitimate and seek to sow chaos. Their history in the United States goes back more than a century to when an anarchist assassinated President William McKinley in 1901.

Today, many young anarchists are members of the Anti-Racist Action, a national network of antifa associations, according to the Southern Poverty Law Center. Critics often denounce antifa followers as anarchists, with Trump blaming the recent violent protests on "radical-left anarchists."

"For the most part, the anarchists we see here in the United States tend to be more disenchanted with the progressive left," said Brian Levin, a professor of criminal justice at California State University.

But anarchists thrive on the right as well. The Bay Area National Anarchists, for example, "envision a future race war leading to neo-tribal, whites-only enclaves to be called "National Autonomous Zones," according to SPLC.