Trump vows military response to muzzle 'domestic terror acts'

President Donald Trump vowed to order a military crackdown on violent once-in-a-generation protests gripping the United States, saying he was sending thousands of troops onto the streets of the capital and threatening to deploy soldiers to states unable to regain control.

The dramatic escalation came a week after the death in Minneapolis of George Floyd, an unarmed black man who was killed when a white police officer knelt on his neck, leading to the worst civil unrest in decades in New York, Los Angeles and dozens of other cities.

After being criticized for his silence on the worsening crisis, Trump struck a martial tone in a nationwide address from the White House garden, as police fired tear gas on peaceful protesters outside the fence.

"I am dispatching thousands and thousands of heavily armed soldiers, military personnel and law enforcement officers to stop the rioting, looting, vandalism, assaults and the wanton destruction of property," Trump said.

He slammed the previous night's unrest in Washington as a "total disgrace" and called on governors to "dominate the streets."

Trump added: "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."

He denounced the protests as "acts of domestic terror."

During his address, however, law enforcers used tear gas to clear protesters outside the White House so Trump could walk across the street to the two-centuries-old St John's church, hit with graffiti and partially damaged by fire during unrest.

"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.

The backlash was swift.

"He's using the American military against the American people," tweeted Democratic presidential hopeful Joe Biden.

"He tear-gassed peaceful protesters and fired rubber bullets. For a photo. For our children, for the very soul of our country, we must defeat him," Biden said.

Thousands of people have participated in the nationwide demonstrations against police brutality and racism since Floyd's killing, making it the most widespread unrest in the United States since 1968, when cities went up in flames over the slaying of civil rights leader Martin Luther King Jr.

Others have seen rage-filled clashes between protesters and police, and widespread property damage. One person was shot dead in Louisville, Kentucky.

Europe, meanwhile, is "shocked and appalled" by the killing of Floyd, the EU's diplomatic chief Josep Borrell said, condemning an "abuse of power."

Borrell urged US authorities to rein in the "excessive use of force" and said the 27-nation bloc supports the right to peaceful protest.

"We here in Europe, like the people of the United States, we are shocked and appalled by the death of George Floyd," Borrell said in Brussels.

And Canberra is investigating a police attack on two Australian television journalists outside the White House.

Foreign minister Marise Payne expressed "strong concerns" about the assault caught live on camera.

"We have asked the Australian embassy in Washington, DC, to investigate this incident," Payne said after the two journalists were slammed with a riot shield, punched and hit with a baton while broadcasting from the protest.

"I want to get further advice on how we would go about registering Australia's strong concerns with the responsible local authorities in Washington," she said, indicating a formal complaint would follow.

Footage showed 7News reporter Amelia Brace being clubbed with a truncheon and cameraman Tim Myers being hit with a riot shield and punched in the face by police clearing Washington's Lafayette Square of protesters on Monday.

The journalists said they were later shot with rubber bullets and tear gassed, which Brace said left the pair "a bit sore."