The move seeks to replicate an operation in the US capital Washington, where Trump deployed National Guard troops and boosted numbers of federal agents, sparking a backlash and a fresh protest on Saturday that drew thousands.

"Chicago about to find out why it's called the Department of WAR," Trump posted Saturday on his Truth Social account.

The Democratic governor of Illinois, where Chicago is located, voiced outrage at Trump's post.

"The President of the United States is threatening to go to war with an American city. This is not a joke. This is not normal," Governor JB Pritzker wrote in a post on X.

"Illinois won't be intimidated by a wannabe dictator," he added.

The post featured an apparent AI image of Trump and the quote: "I love the smell of deportations in the morning" -- both references to the 1979 Vietnam War film "Apocalypse Now".

In the film, the line is spoken by Lt. Col. Bill Kilgore who says he loves the smell of "napalm" -- not "deportations" -- as the American military drops the highly flammable weapon on Vietnamese targets.

The 79-year-old Republican has steadily ramped up threats against Chicago, since an early mention of it at the end of August.

Anti-Trump protesters took to the streets of Chicago on Saturday, carrying signs that read "stop this fascist regime!" and "no Trump, no troops."

The protest route also went past Chicago's Trump tower, and protesters made rude gestures at the president's building as they walked past.

On Saturday in the US capital, where National Guard troops have been deployed since Trump declared a "crime emergency" in August, a thousands-strong protest march wound through downtown with participants demanding an end to the "occupation."

Demonstrators in DC carried inverted US flags as they marched past the country's national monuments, traditionally a symbol of a country facing existential peril.

Trump's troop and federal agent deployments -- which first began in June in Los Angeles, followed by Washington -- have prompted legal challenges and protests, with critics calling them an authoritarian show of force.

Local officials in Los Angeles spoke out against the deployments and the violent tactics employed by ICE agents in Los Angeles, who often wore masks, drove in unmarked cars and chased down and snatched people from the streets without cause or warrants.

In addition to Chicago, Trump has threatened to replicate the surges in Democratic-led Baltimore and New Orleans.

On Friday, Trump signed an order changing the name of the Department of Defense to the Department of War, saying it sends "a message of victory" to the world.

Pentagon chief Pete Hegseth cheered the move, saying the US will decisively exact violence to reach its aims, without apology.