US President Donald Trump signed an order on Monday that will see the National Guard sent to Memphis to combat what his administration says is rampant crime.

Trump, who has already deployed troops to the capital, Washington, D.C., and Los Angeles this year, said he also planned to take similar action in Chicago and elsewhere in the United States.

"We think Chicago is going to be next, and we'll get to St. Louis, and New Orleans," Trump, a Republican, vowed.

The cities in question are all run by Democrats.

What will the National Guard deployment involve?

The deployment of the National Guard is another major test of the limits of presidential power by using military force in US cities.

In the Oval Office alongside Tennessee Governor Bill Lee, also a Republican, Trump signed the initiative which will deploy a broad coalition of federal agencies — including the FBI, Immigration and Customs Enforcement (ICE), the Department of Homeland Security and US Marshals — alongside the National Guard and local law enforcement.

Attorney General Pam Bondi will head the operation, Trump said.

"Memphis had the highest violent crime rate, the highest property crime rate and the third-highest murder rate of any city in the nation," Trump said.

He added that the aim was to stamp out crime, the same reason he cited for last month's troop deployment in Washington, D.C, although city authorities strongly disputed his claims.

"This task force will be a replica of our extraordinarily successful efforts here," Trump said, referring to the National Guard deployment in the US capital. "And, you'll see it's a lot of the same thing."

Is Trump pushing the boundaries of authoritarianism?

US National Guard troops were sent to the streets of Washington, D.C. in August and  Trump took control of its police force, claiming violent crime was out of control.

Armored vehicles were spotted at urban centers and tourist sites around the US capital.

Washington Mayor Muriel Bowser, a Democrat, who denied crime in the city is out of control, described the troop deployment as an "authoritarian push."

Earlier this year, Trump deployed thousands of National Guard troops in Los Angeles to suppress immigration protests.

That move that prompted California Governor Gavin Newsom to accuse the US president of staging a "manufactured crisis," adding the act was "authoritarian."

Edited by: Karl Sexton