Violence erupted in cities across the US on the sixth night of protests sparked by the death in police custody of African-American George Floyd.
Curfews have been imposed in nearly 40 cities, but people have largely ignored them, leading to tense stand-offs.
Riot police clashed with protesters in New York, Chicago, Philadelphia and Los Angeles, firing tear gas and pepper bullets to try to disperse the crowds.
There were multiple instances of police vehicles being vandalised and set alight on Sunday. Riot officers continued to respond with tear gas and flash grenades.
In Philadelphia, local TV stations showed people smashing police cars and looting at least one store.
US President Donald Trump tweeted: “Law & Order in Philadelphia, NOW! They are looting stores. Call in our great National Guard”.
Looting was also reported in Santa Monica, California.
In Minneapolis, where Mr Floyd lost his life, a lorry driver was arrested after reportedly breaching a road barrier before speeding towards a crowd of protesters marching along a major highway.
In Denver, thousands of people protested peacefully in Colorado State Capitol by lying face down with their hands behind their backs and chanting: “I can’t breathe.”
Large-scale protests also took place in Atlanta, Boston, Miami and Oklahoma City.
There were also several reported incidents of riot police responding disproportionately to the demonstrators. In Atlanta, Georgia, two officers were sacked on Sunday for using excessive force – including firing a taser – on two young college students.
The National Guard – the US reserve military force for domestic emergencies – said on Sunday that 5,000 of its personnel had been activated in 15 states and Washington, DC, where crowds once again gathered near the White House, this time lighting fires and throwing stones at riot officers.
“State and local law enforcement agencies remain responsible for security,” the National Guard added.
The Floyd case has reignited US anger over police killings of black Americans. For many, the outrage also reflects years of frustration over socio-economic inequality and segregation, not least in Minneapolis itself.
Hundreds of people have been arrested since the protests began a week ago.
A white ex-policeman has been charged with murdering Mr Floyd, 46, in Minneapolis.
Derek Chauvin, 44, is due to appear in court later on Monday.
It follows the high-profile cases of Michael Brown in Ferguson, Eric Garner in New York and others that have driven the Black Lives Matter movement.