The move seeks to replicate an operation in the US capital Washington, where he has deployed National Guard troops and surged federal agents to conduct arrests and deportations, sparking backlash from local residents.

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

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 film "Apocalypse Now."

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.

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.

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.

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

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