The release of an independent autopsy commissioned by Floyd’s family, which characterised the death as a homicide caused by "asphyxiation from sustained pressure” had already stirred up anger in Minnesota and elsewhere in the US. An official report by the local medical examiner’s office in Minnesota confirmed that the death was homicide.

Speaking to NBC, Bowser said earlier on Monday that protesters had brought “tools and supplies” and used diversionary tactics to evade police.

“They went to different parts of the city, so we think there was a mix of people here but certainly people here who do this type of protest demonstration,” Bowser said.

“We’ve seen some of these tactics before, so we know that they were among the groups here,” the mayor said, blasting “the types of tools they used, restocking, setting fires here and there to draw in the police to various locations”.

The defaced monuments on Washington’s National Mall – for decades, a venue for mostly peaceful protests – included the Lincoln Memorial and the World War II Memorial.

Trump slammed for bible photo op in front of riot-damaged church

Firefighters also extinguished a blaze set in the basement of the historic St John’s Episcopal Church across the street from the White House, where every president since James Madison had attended services at least once.

After his address, riot police used tear gas, rubber bullets and flash bangs to disperse protesters gathered outside the White, so Trump could walk across the street to St Johns church for a photo opportunity.

“We have a great country,” Trump declared as he stood before the church’s boarded up windows, held up a Bible and posed for photographs.

Democratic presidential hopeful Joe Biden slammed Trump for “using the American military against the American people”.

“For our children, for the very soul of our country, we must defeat him,” Biden said in a Twitter message.

02:28

Trump threatens to use military to 'quickly solve' violent unrest in US cities

Trump threatens to use military to 'quickly solve' violent unrest in US cities

Outrage over the recent deaths of black Americans had been building for months in the US.

Floyd, 46, died after he was arrested on May 25 outside a shop in Minneapolis, following a report by an employee of the shop that Floyd tried to use a counterfeit US$20 bill. Footage of the arrest shows a white police officer, Derek Chauvin, kneeling on Floyd's neck for nearly nine minutes while he was pinned to the ground.

Chauvin, 44, was one of four officers on the scene who were fired from the Minneapolis police force. But he is so far the only one to be officially charged: the Hennepin County district attorney indicted him for third-degree murder and second-degree manslaughter. Chauvin was also accused of ignoring another officer who warned him about Floyd’s safety after Floyd was handcuffed on the ground and pleading that he could not breathe.

‘Like a civil war’: how the world is reacting to the US protests

"There is no other health issue that could cause or contribute to the death," said Dr Michael Baden, one of the independent medical examiners hired by Floyd’s family. "Police have this false impression that if you can talk, you can breathe. That's not true."

After the release of that assessment, the Hennepin county medical examiner in Minnesota released a report confirming that Floyd’s death was a homicide resulting from being restrained, explaining that the cause of death was “cardiopulmonary arrest complicating law enforcement subdual, restrain, and neck compression”.

Anger over the shooting death of another unarmed black man, Ahmaud Arbery, 25, during an encounter with two white men in Georgia on February 23, was still simmering in the US when Floyd’s deadly encounter with police occurred last week.

Arbery’s assailants, a father and his adult son, were not arrested until May 7, after local protests about the killing gained momentum.

And Breonna Taylor, a 26-year-old emergency medical technician, had been sleeping slightly after midnight on March 13 when plain clothes officers using a “no-knock” search warrant burst into her Kentucky home and shot her eight times, killing her.

Trump rushed to underground bunker as protests raged in Washington

Throughout the weekend and into Sunday night in Washington, protesters and police had clashed sporadically in Lafayette Square, across Pennsylvania Avenue from the White House, prompting Trump to call for “LAW & ORDER!” in a Twitter post.

Trump had reportedly been moved to an on-site bunker for safety on Friday night, and the lights of the White House were turned off on Sunday night.

Bowser shot back at Trump’s accusation that the mayor was not allowing city police to help the Secret Service bring the unrest under control.

Washington’s police department “will always protect DC and all who are in it whether I agree with them (such as those exercising their First Amendment Right) or those I don't (namely, @realdonaldtrump)”, the mayor said on Twitter.

On Monday, Trump told governors on a video teleconference call that they “have to get much tougher”.

More than 4,000 people were arrested in US cities over the weekend, according to Associated Press, after protests that turned violent sent smoke billowing over urban skylines from Philadelphia, Pennsylvania, to Salt Lake City, Utah.

Trump calls governors ‘weak’, urging crackdown on George Floyd protests

It is the first time since 1968, the year when civil right activist Martin Luther King Jnr was assassinated, that so many local leaders have issued curfews in the face of civic unrest, according to The New York Times.

A man was killed in Louisville, Kentucky, soon after midnight on Monday during a protest in the city, after being shot by local police and National Guard personnel.

“Officers and soldiers began to clear the lot and at some point were shot at,” Louisville police chief Steve Conrad was quoted by the Courier-Journal as saying. “Both [Louisville Metro Police Department] and National Guard members returned fire.”

It was unclear whether the dead man, David McAtee, had fired at the officers. Kentucky Governor Andy Beshear ordered Kentucky State Police to investigate the incident, the newspaper said.

Governors of more than half of America’s states have called in the National Guard to help curb the unrest.

Hundreds were arrested in New York City over the weekend after peaceful protests turned into violent clashes with police and demonstrators failed to disperse, according to local media reports.

In Santa Monica in Southern California, looters broke into shops in the area’s upscale business district, stealing items and setting fires, The Los Angeles Times reported.

The outcry over Floyd's death spread to Europe over the weekend, with protesters taking to the streets in London, Berlin and Copenhagen, Denmark, to show solidarity with those demonstrating in the US.

In Germany, soccer stars knelt in support of the actions. Memorial graffiti of Floyd has been put up in Berlin's famous Mauerpark, where street artists paint sections of the former Berlin Wall.

In London, hundreds marched outside the US embassy. The BBC reported that protesters held up placards saying “racism has no place”, and “I can't breathe” – a reference to Floyd's words during his arrest.

Additional reporting by Stuart Lau and Agence France-Presse