President Donald Trump has threatened to send in the military to quell growing civil unrest in the US over the death of a black man in police custody.
He said if cities and states failed to control the protests and "defend their residents" he would deploy the army and "quickly solve the problem for them".
Protests over the death of George Floyd have escalated over the past week.
Presidential candidate Joe Biden criticised Mr Trump on Tuesday for "serving the passions of his base".
"We're not going to allow any president to quiet our voice," the Democrat said, referencing the US constitution which guarantees protestors' freedom to assemble.
On Tuesday the Las Vegas sheriff said an officer died in a shooting after police attempted to disperse a crowd.
Dozens of people have been injured as authorities used tear gas and force to disperse protests which have swept more than 75 cities.
Four officers meanwhile were shot and injured on Monday night during unrest in St Louis, Missouri.
Dozens of major cities have imposed overnight curfews.
In New York on Monday night, the iconic department store Macy's was broken into, as shops were looted and windows smashed
Curfew in the city will resume at 20:00 (midnight GMT) on Tuesday
In Chicago, two people were reported killed amid unrest, although the circumstances are unclear
The chief of police in Louisville, Kentucky has been sacked after law enforcement officers fired into a crowd on Sunday night, killing the owner of a nearby business
Australian PM Scott Morrison has demanded an investigation into the alleged assault by police of two Australian journalists covering protests in Washington DC
Music channels and celebrities have pledged to mark Blackout Tuesday, pausing for eight minutes - the length of time a police officer knelt on Mr Floyd's neck
The protests began after a video showed Mr Floyd, 46, being arrested in Minneapolis on 25 May and a white police officer continuing to kneel on his neck even after he pleaded that he could not breathe.
The officer, Derek Chauvin, has been charged with third-degree murder and will appear in court next week. Three other police officers have been fired.
The Floyd case has reignited deep-seated anger over police killings of black Americans and racism. It follows the high-profile cases of Michael Brown in Ferguson, Missouri; Eric Garner in New York; and others that have driven the Black Lives Matter movement.
For many, the outrage also reflects years of frustration over socio-economic inequality and discrimination, not least in Minneapolis itself.