Two hundred Texas National Guard troops have arrived in Illinois, a Pentagon official said, ahead of a planned deployment in Chicago that is strongly opposed by local Democratic officials.
US President Donald Trump has already sent troops onto the streets of Los Angeles and Washington and has ordered them to Memphis, as well as Chicago and Portland, threatening to invoke emergency powers to forward such efforts if the courts get in the way.
The moves comes as around 58% of Americans - including seven in ten Democrats and half of Republicans - think the president should send armed troops only to face external threats, a poll suggests.
The Reuters/Ipsos poll poll, which was conducted between Friday and yesterday, also showed the Republican president's approval rating ticking down to 40% - one percentage point lower than in a late September poll, with his rating slipping on his handling of crime and the cost of living for US households.
The poll was carried in the days after Mr Trump told an unusual meeting of hundreds of generals and admirals summoned from around the world to Virginia that the US faces an "enemy within" and as he deploys armed troops to patrol a growing number of Democratic-led cities.
Democratic leaders say the deployments are politically motivated and have challenged the troop movements in court.
Some 37% of poll respondents said they agreed with a statement that presidents of either political party should have the power to deploy troops into states even when state governors object, compared to 48% who disagreed.
The US military traditionally keeps itself far removed from political discussions, and the Reuters/Ipsos poll showed Americans prefer that approach.
Some 83% of respondents said the military "should remain politically neutral and not take a side in domestic policy debates" while 10% said the armed forces should start taking sides and support the president's domestic policy agenda.
About one in five Republicans said the military should take the president's side in political debates.
The troops from Texas were sent to Illinois as part of a mission to protect "federal functions, personnel, and property," the Pentagon official said on condition of anonymity, adding that the Guardsmen had been mobilised for an initial period of 60 days.
The troops were seen at a military facility in Elwood, southwest of Chicago.
The planned deployment of those forces has infuriated Democratic Governor JB Pritzker, who said they "should stay the hell out of Illinois," and that any deployment against his state government's wishes would amount to an "invasion."
Mr Trump authorised at the weekend the deployment of 700 National Guard troops to Chicago, sparking a lawsuit by Illinois state officials who accused him of using US troops "to punish his political enemies."
"The American people, regardless of where they reside, should not live under the threat of occupation by the United States military, particularly not simply because their city or state leadership has fallen out of a president's favour," the Illinois Attorney General and counsel for Chicago said.
However, Judge April Perry, an appointee of Mr Trump's Democratic predecessor Joe Biden, declined to issue an immediate temporary restraining order, instead scheduling a full hearing for tomorrow.
Homeland Security Secretary Kristi Noem has defended the plan to send troops to Chicago, claiming that the third-largest US city is "a war zone."
Mr Trump has similarly taken aim at Portland, which like Chicago has seen surges of federal agents as part of the president's mass deportation drive, prompting protests outside immigration processing facilities.
Mr Trump asserted that it is "war-ravaged" and riddled with violent crime.
But in a Saturday court order temporarily blocking the deployment of troops to Oregon, US District Judge Karin Immergut wrote that "the President's determination was simply untethered to the facts."
Protests in Portland did not pose a "danger of rebellion" and "regular law enforcement forces" could handle such incidents, Judge Immergut wrote.
Mr Trump responded to that setback by openly mulling the use of the Insurrection Act - which allows the president to deploy the military within the United States to suppress rebellion - in order to send more troops into Democratic-led US cities.
"We have an Insurrection Act for a reason," Mr Trump said, adding that he would use it if "people were being killed and courts were holding us up or governors or mayors were holding us up."
