WASHINGTON - The United States teetered on the brink of its most serious internal conflict in decades on Monday (June 1) evening as President Donald Trump said he was “dispatching thousands and thousands of heavily armed soldiers, military personnel and law enforcement officers to stop the rioting, looting, vandalism, assaults and wanton destruction of property” in Washington, DC.

He vowed to do the same in other cities if mayors and governors fail to regain control of the streets as nationwide protests entered their sixth day.

As he spoke in the Rose Garden minutes before a 7pm curfew was to come into effect, military and mounted police used tear gas and rubber bullets to push back protesters who ran helter-skelter through the capital’s shuttered downtown. Explosions could be heard in the Rose Garden.

The protests were mostly peaceful - a characteristic of the demonstrations across dozens of cities in recent days since the death of Mr George Floyd, a 56-year-old black man, while restrained in police custody in Minneapolis a week ago. A police officer had placed a knee on Mr Floyd’s neck for several minutes.

An independent autopsy ordered by Mr Floyd’s family and released on Monday concluded that he died from “mechanical asphyxiation”, meaning his oxygen supply was cut off.

Derek Chauvin, the police officer who knelt on Mr Floyd’s neck, and three others who stood by, were swiftly fired, but it took four days to charge Chauvin with third degree murder. He was arrested and on Monday transferred to a maximum security prison.

The other three officers have not been charged – a continuing source of outrage for the protesters.

The protesters have comprised not just African Americans but also to a large extent white people and also, by and large, young people.

They have been largely peaceful during the day, but turned violent mostly after dark when stores and buildings were looted and torched.

The administration blamed radical left wing and anarchist groups for the destruction, which hit several cities. State authorities have also said the violence was perpetrated by elements other than the protesters.

“In recent days, the nation has been gripped by violent anarchists,” Mr Trump said. “What happened in the city (Washington) last night was a total disgrace.”

“Mayors and governors must establish an overwhelming law enforcement presence until the violence has been quelled,” he 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.”

On Sunday night in Washington, protesters set fires outside the White House and clashed with police.

There were clashes and looting overnight in a slew of other cities as well, from New York to Philadelphia to Atlanta – all of which again saw protesters gathering on Monday, in defiance of curfews.

Missouri state’s St. Louis police said late Monday night that four police officers had been struck by gunfire in an ongoing 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.

Earlier on Monday, Mr Trump told state governors in a conference call that they were weak to have lost control of the streets.

“If you don’t dominate, you’re wasting your time,” he told them. “They’re going to run over you, you’re going to look like a bunch of jerks.”

During the day, Mr Floyd’s brother, speaking in Minneapolis, called for a stop to violence.

Former president Barack Obama said in a statement: “The waves of protests… represent a genuine and legitimate frustration over a decades-long failure to reform police practices and the broader criminal justice system in the United States.

“The overwhelming majority of participants have been peaceful, courageous, responsible, and inspiring.”

But he added: “The small minority of folks who’ve resorted to violence in various forms, whether out of genuine anger or mere opportunism, are putting innocent people at risk, compounding the destruction of neighbourhoods that are often already short on services and investment and detracting from the larger cause.”

The UN rights chief said on Tuesday (June 2) the pandemic’s disproportionate impact on ethnic minorities in the US and the protests triggered by George Floyd’s death were exposing “endemic inequalities” that must be addressed.

“This virus is exposing endemic inequalities that have too long been ignored,” Michelle Bachelet said in a statement. She added that “in the United States, protests triggered by the killing of George Floyd are highlighting not only police violence against people of colour, but also inequalities in health, education, employment and endemic racial discrimination”.

Analysts see this as a pivotal moment in a country already under severe stress from the Covid-19 pandemic that has killed well over 100,000 people and crashed the economy, leaving some 40 million unemployed.

That has come on top of a severely polarised, toxic political environment heading into a presidential election on Nov 3 which is seen as one of the most critical in the nation’s modern history.

“How do you tell other countries that America is a democracy to be emulated when this is what is happening on the ground in the United States?” tweeted Dr Ian Bremmer, chief executive officer of The Eurasia Group.

“From the global perspective… the biggest problem is America’s… ability to lead by example which has been eroding for certainly a decade plus but much more quickly now. You can say it’s all about President Trump but in my view it’s a lot deeper and more structural.”