Police fired tear gas outside the White House late Sunday as anti-racism protestors again took to the streets to voice fury at police brutality, and major US cities were put under curfew to suppress rioting.
With the Trump administration branding , there were more confrontations between protestors and police and fresh outbreaks of looting.
Violent clashes erupted repeatedly in a small park next to the White House, with authorities using tear gas, pepper spray and flash-bang grenades to disperse crowds who lit several large fires and damaged property.
Protesters confront police outside the White House. Source: EPA
Washington police said a fire was intentionally set at the historic St. John’s Episcopal Church, which is located near the White House.
Aerial footage posted to social media also appeared to show smoke from several fires rising up around the Washington Monument.
Local US leaders appealed to citizens to give constructive outlet to their rage over the death of unarmed black man George Floyd in Minneapolis, while night-time curfews were imposed in cities including Washington, Los Angeles and Houston.
Two nights earlier, US President Donald Trump was reportedly for about an hour as the protests escalated.
Curfews are now in place across 20 US states and thousands of National Guard troops have been unleashed on major cities as demonstrators continue to take to the streets following Mr Floyd's death.
Speaking live on television on Sunday evening, Minneapolis's police chief Medaria Arradondo said he believed the three officers who stood by as Derek Chauvin held his knee on Mr Floyd's neck for nine minutes were "complicit" in his death.
Mr Chauvin has been arrested and charged with third-degree murder and manslaughter, but the other three officers have not been charged.
"Being silent or not intervening, to me, you're complicit. I don't see a level of distinction," Mr Arradondo told CNN.
"If there were one solitary voice that would have intervened in that, that's what I would have hoped for. That did not occur.
"To the Floyd family, I want you to know, my decision to fire all four officers was not based on some sort of hierarchy. Mr Floyd died in our hands, and so I see that as being complicit."
A tanker truck moving at high-speed also ploughed into a highway full of protesters in Minneapolis.
Local media showed footage of thousands of people rushing to either side of the highway before the truck came barrelling down the middle of the road.
Protesters quickly dragged the driver out of the car before he was arrested by police, who took him to a local hospital with non-life threatening injuries.
"The incident just underscores the volatile situation we have out there," Minnesota Governor Tim Walz told a news conference, adding he did not know the motives of the driver.
In Atlanta, a video showed police officers using tasers in an attempt to get two people out of a car during a protest.
Local media, who were broadcasting nearby, said the officers smashed in the windows and flattened the car tires before arresting one woman and one man, who they tasered in the process.
Lori Lightfoot, the mayor of Chicago, said her city was sharply limiting access to its central business district after violent protests. She reflected the exasperation of many officials and ordinary residents over the turn from peaceful protest to explosive violence.
She told CNN: "I am hurt and angry at those who decided to try to hijack this moment and use it as an opportunity to wreak havoc, to loot and to destroy. You should be ashamed of yourselves. What you have done is to dishonour yourself, your family and our city."
Meanwhile, US National Security Advisor Robert O'Brien has denied the existence of systemic racism in police forces across the US.
The fourth in a string of chief security advisors to Mr Trump over the past three years, Mr O'Brien claimed there were only "a few bad apples" among police ruining the reputation of the vast majority.
"No, I don't think there's systemic racism. I think 99.9% of our law enforcement officers are great Americans. Many of them are African American, Hispanic, Asian, they're working the toughest neighbourhood, they've got the hardest jobs to do in this country and I think they're amazing, great Americans," he told CNN.
"There are some bad cops who are racist. There are cops that maybe don't have the right training."
Mr Walz extended a curfew for a third night Sunday and praised police and guardsmen for holding down violence, saying: "they did so in a professional manner. They did so without a single loss of life and minimal property damage."
"Congratulations to our National Guard for the great job they did immediately upon arriving in Minneapolis, Minnesota, last night," Mr Trump said in a tweet, adding that they "should be used in other States before it is too late!"
National Guard deployed
The Department of Defense said that around 5,000 National Guard troops had been mobilised in 15 states as well as the capital Washington with another 2,000 on standby.
The widespread resort to uniformed National Guards units is rare, and it evoked disturbing memories of the rioting in US cities in 1967 and 1968 in a turbulent time of protest over racial and economic disparities.
Multiple arrests were reported by US media in Minneapolis, Seattle and New York as rallies continued through the night.
Officers in Los Angeles fired rubber bullets and swung batons during a testy standoff with demonstrators who set fire to a police car.
But Atlanta Mayor Keisha Lance Bottoms said that Mr Trump, who has often urged police to use tough tactics, was not helping matters.
"We are beyond a tipping point in this country, and his rhetoric only enflames that," she said on CBS. "And he should just sometimes stop talking."
'Not turning the cheek'
Peaceful protests occurred too, including in Toronto as the movement spread beyond America's borders.
Demonstrators nationwide chanted slogans such as "Black Lives Matter" and "I can't breathe," which Mr Floyd was heard saying repeatedly in his final moments, as he lay, handcuffed, on the ground with Mr Chauvin's knee on his neck.
"We're not turning the cheek anymore. Black lives matter," said makeup artist Melissa Mock, who joined several thousand in a daytime protest in Miami.
Earlier, people congregated and chanted peacefully in Minneapolis, carrying brooms to help clean up damaged shops and streets.
Some placed flowers in front of the shop where Mr Floyd was arrested last week.
'A nation in pain'
There was looting in Miami, where a curfew had been announced. Houston police made more than 130 arrests.
The Denver mayor said people had been stopped while bringing "assault weapons, handguns (and) baseball bats" into the city. And Los Angeles expanded its curfew order as looting broke out.
In New York, Mayor Bill de Blasio said a video showing a police car forcing its way through protesters in Brooklyn was "upsetting" but that he did not blame the officers, who faced "an extremely dangerous situation."
But unlike other mayors, Mr de Blasio declined to declare a curfew and said he opposed bringing in "outside military forces" to help local police.
"If you're bringing outside military or police forces you actually endanger the safety and security of New Yorkers because they're not trained to handle the realities of our streets and our communities," he told reporters.
Joe Biden, Mr Trump's likely Democratic opponent in November's presidential election, visited the scene of one anti-racism protest on Sunday.
"We are a nation in pain right now, but we must not allow this pain to destroy us," Mr Biden tweeted, posting a picture of him speaking with an African-American family at the site where protesters had gathered in Delaware late Saturday.
Hundreds of Londoners defied coronavirus restrictions and rallied outside the US embassy on Sunday in solidarity with US protesters.
In Germany, thousands rallied outside the US embassy in Berlin, while England football international Jadon Sancho marked one of his three goals for Borussia Dortmund against Paderborn by lifting his jersey to reveal a T-shirt bearing the words "Justice for George Floyd".
With additional reporting from Reuters, Claudia Farhart.