President Donald Trump has said he was withdrawing National Guard troops from Chicago, Los Angeles and Portland, following a series of legal setbacks over his military deployments in US cities.

"We are removing the National Guard from Chicago, Los Angeles, and Portland, despite the fact that CRIME has been greatly reduced by having these great Patriots in those cities, and ONLY by that fact," Trump said on his Truth Social network.

Trump said the three cities "were GONE if it weren't for the Federal Government stepping in."

"We will come back, perhaps in a much different and stronger form, when crime begins to soar again - Only a question of time!" Trump added.

The Republican president sent troops into the three cities run by Democrats for what he said was a crackdown on illegal immigration and crime in the first year of his second term in the White House.

Local leaders slammed the moves as authoritarian overreach and launched a string of legal challenges, with the US Supreme Court last week blocking the Chicago deployment.

Overstepping authority

Judges overseeing lawsuits filed by cities challenging the deployments have consistently ruled that the Trump administration overstepped its authority and found that there is no evidence to support claims that troops are necessary to protect federal property from protesters.

Trump started deploying troops in June amid protests against his hardline immigration policies, including efforts to ramp up deportations.

He also deployed troops to Washington and took control of local police in response to what he said was rampant crime, though local crime statistics indicated otherwise, using his unique authority as president over the US capital.

Military officials have been winding down and scaling back the deployments in recent months as litigation has left them in limbo.