Washington, Jun 3 (IANS): US 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", the BBC reported.

Protests over the death of George Floyd have escalated over the past week.

Presidential candidate Joe Biden criticised 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.