US President Donald Trump on Monday threatened the deployment of the military to quell the nationwide protests over the death of George Floyd, the black man who died in police custody last week in Minneapolis, reported Xinhua news agency.

"If a city or state refuses to take the actions 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," Trump said at the White House Rose Garden. It was his first speech since Floyd's death on May 25.

At one time during his speech, Trump said he might invoke the rarely-used Insurrection Act of 1807, which authorises the president to unilaterally deploy military forces on domestic soil for law enforcement purposes. Trump claimed he would send in "thousands and thousands of heavily armed soldiers, military personnel and law enforcement officers" to restore order.

With helicopters hovering above and successive bangs from the nearby Lafayette Square, Trump declared himself "your president of law and order" and an "ally of all peaceful protesters." Just as he spoke, protesters gathering near the White House were being dispersed by police using tear gas and rubber bullets.

Thanks to the police's effort to clear the path, Trump was later able to cross H Street to visit St. John's Episcopal Church, where he stood for a photo opportunity along with some senior administration officials.

The church, a historical landmark, was partially damaged as protesters set up fire nearby during Sunday night's unrest.

New York Governor Andrew Cuomo condemned Trump's remarks, saying at a news conference shortly afterward that "calling out the American military for a photo opportunity. That's what it was. I mean, it was shameful. It was really, truly shameful."

Earlier on Monday, Trump reportedly called state governors "weak" in a contentious phone call with them to discuss the ongoing chaos, urging the state leaders to "dominate" to prevent further violence.

White House Press Secretary Kayleigh McEnany said during a press briefing Monday that by using the word "dominate" Trump meant keeping peace on streets, not the way to handle protesters.

"The president has made clear that what we are seeing on America's streets is unacceptable," McEnany said. "Violence, looting, anarchy, lawlessness are not to be tolerated."

Curfews have been imposed on Washington, D.C. for Monday and Tuesday, effective from 7 pm local time and running through the night.

Floyd, 46, died after Minneapolis police officer Derek Chauvin kept kneeling on his neck for almost nine minutes. Two separate autopsies released Monday both found that Floyd's death was a homicide.

--BERNAMA