Protesters of #BlackLivesMatter tear gassed in Washington

Largely peaceful protesters near the White House were repelled with tear gas and mounted police on Monday as President Donald Trump spoke in the Rose Garden, live televised images showed.

Trump said he was mobilising all federal resources to suppress protests that have erupted since the death of George Floyd in Minneapolis after a police officer pinned him to the ground with a knee on his neck. 

Law enforcement, including officers on horseback, moved on protesters in Lafayette Park.

The police action against protesters cleared the way for Trump to walk from the White House to nearby St John's Episcopal Church along with other officials, including US Attorney General William Barr. Trump posed for photos at the church, which suffered minor damage the night before, holding up a Bible.

The security forces that moved against protesters at the White House included National Guard military police, Secret Service, Department of Homeland Security police as well as District of Columbia police.

Trump threatens military deployment

The president pledged to end six nights of looting and violence in major cities across the nation "now," saying he would deploy the US military if state governors refused to call out the National Guard.

"Mayors and governors must establish an overwhelming law enforcement presence until the violence has been quelled," Trump said. "If a city or state refuses to take the actions that are necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them."

Just a few hours later, thousands of people marched through the streets of Brooklyn, shouting "justice now" while cars drove alongside, some drivers honking in support while police vans followed.

A smaller march took place in Hollywood, where protesters defied a curfew imposed by Los Angeles Mayor Eric Garcetti to march to a line of police, where they knelt down with their arms raised.

Four officers hit by gunfire in St. Louis – police

Missouri state's St Louis police said late Monday night four police officers had been struck by gunfire in a clash between protesters and the police.

The officers have been transported to an area hospital and their injuries were believed to be "non-life threatening", police said in a tweet.

'Mechanical asphyxiation'

Anti-police brutality marches and rallies, which have turned violent after dark each night over the last week, erupted over the death of George Floyd, a 46-year-old African American who died in Minneapolis police custody after being pinned beneath a white officer's knee for nearly nine minutes.

A second autopsy ordered by Floyd's family and released on Monday found that his death was a homicide by "mechanical asphyxiation," meaning that physical force interfered with his oxygen supply. The report says three officers contributed to Floyd's death.

The Hennepin County Medical Examiner then released details of its autopsy findings that also said Floyd's death was a homicide caused by asphyxiation. The county report added that Floyd suffered cardiopulmonary arrest while being restrained by police and that he had arteriosclerotic and hypertensive heart disease, fentanyl intoxication and recent methamphetamine use.

Derek Chauvin, the 44-year-old Minneapolis police officer who kneeled on Floyd, was arrested on third-degree murder and second-degree manslaughter charges. Three other officers involved in the arrest have not been charged.

Floyd's death was the latest case of police brutality against black men caught on videotape and prompting an outcry over racism in US law enforcement. It reignited simmering racial tensions in a politically divided country that has been hit hard by the pandemic, with African-Americans accounting for a disproportionately high number of cases.

Dozens of cities order curfews

Dozens of cities across the United States remain under curfews not seen since riots after the 1968 assassination of Martin Luther King Jr. The National Guard deployed in 23 states and Washington, DC.

The curfews were imposed as most Americans were still emerging from weeks of strict "stay-at-home" orders imposed in the face of the coronavirus pandemic. On Monday, dozens of people paid their respects to Floyd outside Cup Foods, the scene of his death, leaving flowers and signs. A little girl wrote “I’ll fight with you” in aqua blue chalk in the road.

“This is therapeutic. My heart was real heavy this morning so I came down extra early and when I got here, the heaviness lifted,” said Diana Jones, 40, the mother of four children. “This right here lets me know that things are going to be OK.”

Terrence Floyd, the victim's brother, told the gathering he wanted people to get educated and vote rather than resort to violence and destruction. "Let's do this another way," he said.

Trump, a Republican, has condemned the killing of Floyd and promised justice but has described protesters as "thugs".

Opponents accuse him of stoking conflict and racial tension when he should be uniting the nation and addressing underlying issues, and his campaign-style appearance at St. John's Church sparked criticism.

"I am outraged," Bishop Mariann Edgar Budde of the Episcopal Diocese of Washington, which includes the church, said on CNN. Trump's message was antithetical to church teachings, she said.

New York Governor Andrew Cuomo criticised the use of force against demonstrators to make way for Trump to hold the picture-taking opportunity.

"It was really, truly shameful,” he said.