The US will designate the anti-fascist group Antifa a terrorist organisation, President Donald Trump says.
The president accused Antifa of starting riots at street protests over George Floyd’s death.
Mr Floyd, a black man, died in police custody earlier this week, reigniting anger at police treatment of African-Americans.
Protests over his death have turned violent, prompting major cities to impose curfews.
The National Guard – the US reserve military force for domestic emergencies – had been deployed in 15 states to help police forces deal with the unrest.
In Minneapolis, where Mr Floyd died on Monday after a white police officer put his knee on his neck for more than eight minutes, there have been five nights of arson and looting.
US officials have given contrasting explanations for who is responsible for the riots, with some suggesting outside groups and individuals were involved.
On Saturday, Minnesota’s Democratic Governor Tim Walz suggested that foreign influences, white supremacists and drug cartels were behind the violence, giving few other details.
On Twitter Mr Trump blamed “Antifa-led anarchists” and “Radical Left Anarchists” for the unrest, again without providing more specifics.