Donald Trump has announced a “surge” of hundreds of law enforcement officers into Democratic-run cities including Chicago, drawing condemnation from civil liberties watchdogs.

The US president’s move came after a crackdown by federal agents on anti-racism protesters in Portland, Oregon, and was consistent with his emphasis on “law and order” as a key component of his reelection campaign.

“Today, I’m announcing a surge of federal law enforcement into American communities plagued by violent crime,” Trump said at the White House on Wednesday. “We’ll work every single day to restore public safety, protect our nation’s children and bring violent perpetrators to justice.”

The aggressive move renewed fears of an expanding state security apparatus threatening the rights of peaceful demonstrators. The American Civil Liberties Union tweeted: “We will continue to defend our constitutional rights from Trump’s lawlessness — in Portland, Chicago, and wherever else necessary.”

With just over a hundred days until the presidential election, Trump has argued that violence would worsen if his Democratic rival, Joe Biden, is elected. He cast the latest move in starkly political partisan terms.

“My administration will be working to remove dangerous offenders sprung loose by these deadly policies and, frankly, by these deadly politicians,” he said. “America must be a sanctuary for law-abiding citizens, not criminal aliens. My vision for America’s cities could not be more different from the lawlessness being pushed by the extreme radical left.”

The FBI, Drug Enforcement Administration, US Marshals Service and Department of Homeland Security would all send agents to Chicago, Trump added, giving a lengthy description of recent violence in America’s third biggest city and accusing its Democratic leaders of failing residents.

“No mother should ever have to cradle her dead child in her arms simply because politicians refused to do what is necessary to secure their neighborhood and to secure their city,” he said.

The announcement pits Trump against Lori Lightfoot, the mayor of Chicago, who has made clear her opposition to federal intervention. “Under no circumstances will I allow Donald Trump’s troops to come to Chicago and terrorize our residents,” she tweeted on Tuesday.

Yet on Wednesday, the president denied the initiative was a political stunt and claimed Chicago actually wanted his help. “The cities, unfortunately, that are in trouble are all run by Democrats. You have radical-left Democrats running cities like Chicago and so many others … Unfortunately, that’s the way it is. I mean, that’s the facts.

”Mayor Lightfoot sent me a letter yesterday, and I think, in their own way, they want us to go in. There’ll be a time when they’re going to want us to go in full blast, but right now we’re sending extra people to help. We’re arresting a lot of people that have been very bad.”

He added: “She’s a Democrat. She’s making a big mistake. People are dying in Chicago and other cities, and we can solve the problem.”

A reporter challenged Trump over why he blamed his predecessor, Barack Obama, for a rise in crime in Chicago in 2016, yet does not accept responsibility now. He replied: “Because President Obama was invited in, and he did a poor job. President Obama could have gone into Chicago. He could have solved the problem, and he didn’t. In our case, they don’t want us in. We can solve the problem very easily.”

The president and William Barr, the attorney general, also announced on Wednesday that two dozen agents would be dispatched to Albuquerque, New Mexico.

Barr said: “Today, we have extended Operation Legend to Chicago and Albuquerque to protect the residents of those cities from senseless acts of deadly violence by targeting those involved in gang activity and those who use guns to commit violent crime.”

The justice department says Chicago is experiencing a significant increase in violent crime, with murders currently up 51% over 2019, while Albuquerque is on pace to break 2019’s record for murders in the city.

Martin Heinrich, a Democratic senator for New Mexico, condemned the intervention. “Instead of collaborating with the Albuquerque police department, the sheriff is inviting the President’s stormtroopers into Albuquerque,” he said.

The president has linked the growing violence in the streets with protests against racial injustice in what critics say is a ploy to stoke fears in predominantly white suburbs. Experts in criminal justice say the rise in crime is more complex, especially in the context of the coronavirus pandemic and economic slump.

The unrest in Portland only grew after federal agents in camouflage were seen taking people away in unmarked cars without probable cause. Several lawsuits have been filed questioning the federal government’s authority to use broad policing powers in cities.

Democratic mayors of 15 cities, including Portland, have condemned the use of the agents in a letter to Barr and the acting homeland security secretary, Chad Wolf.

The announcement on Wednesday marked an expansion of a justice department programme launched by Barr on 8 July. “Operation Legend” was initially devised to address violent crime in Kansas City, Missouri, and named after LeGend Taliferro, a four-year-old boy fatally shot there last month. The first federal arrest under Operation Legend was announced on Monday.

Leon Panetta, a former defence secretary and CIA director, said: “One of the last holdouts for tyrants is to try to have the military be able to protect them, and that fear that he may try to do that raises a lot of concerns about just how far will he go to try to ‘take over’ a lot of these cities and states in terms of their ability to conduct law enforcement on their own.”

Panetta added: “It’’s interesting because federalism has always been a calling card for Republicans to avoid having the federal government impose its will on states and communities. To have a president who’s prepared to send federal officers into these communities I think represents a step that ought to not only create fear in the people that are impacted by that decision, but should raise a hell of a lot of fear for those Republicans who have defended federalism most of their lives.”