Trump has succeeded in ordering troops onto the streets of three US cities -- Los Angeles, Washington and Memphis -- while judges have so far blocked National Guard forces from operating in Portland and Chicago.

"Tennessee Guardsmen and women are currently assisting with tasks such as community safety patrols, site security, and traffic control in support of ongoing efforts to reduce crime and promote public safety in Memphis," the Tennessee Military Department said.

The troops are "under federal orders from the president and authorization from (Tennessee Republican) Governor Bill Lee," the department said.

The US president -- who has exaggerated the scale of unrest to justify ordering deployments that have largely been opposed by local Democratic leaders -- suggested late last month that American cities be used as "training grounds" for the country's military forces.

After the Portland deployment was temporarily blocked in court, Trump openly mulled the use of the Insurrection Act -- which allows the president to deploy the military within the United States to suppress rebellion -- to send more troops into Democratic-led US cities.

On Thursday, a US appeals court declined to lift a lower court's block on deploying troops to Chicago, saying Trump's administration had not demonstrated that conditions in the Illinois city justify such a move.

"Even after affording great deference to the president's evaluation of the circumstances, we see insufficient evidence of a rebellion or danger of rebellion in Illinois," the court said.

"The spirited, sustained, and occasionally violent actions of demonstrators in protest of the federal government's immigration policies and actions, without more, does not give rise to a danger of rebellion against the government's authority."

Trump has been accused by critics of growing authoritarianism as he seeks to deport undocumented immigrants through raids by armed and masked federal agents, which have sparked allegations of rights abuses and illegal detentions.