The mayor of Newark, New Jersey, said an immigration raid in the city was done without a warrant, and led to the detainment of undocumented residents as well as citizens.

Newark mayor Ras Baraka said that Immigration and Customs Enforcement (Ice) had raided a local establishment. “Newark will not stand by idly while people are being unlawfully terrorized,” he wrote in a statement.

The mayor’s announcement came as major cities across the US braced for Ice raids, as promised by Donald Trump’s border czar Tom Homan, who has said the federal government will uphold Trump’s promise of “mass deportations”. Homan has signaled that so-called sanctuary cities – localities that have refused to hand over immigrants to federal authorities – would be early targets for raids.

Ice announced it has made a total of 538 arrests in a Thursday update. The agency did not immediately respond to the Guardian’s query about when and where in the US the arrests were made.

The numbers are not necessarily exceptional – the agency averaged more than 450 arrests a day in 2023, when Joe Biden was president, for instance. But the agency’s movements have drawn particular focus amid the Trump administration’s immigration crackdown. Since taking office on Monday, the president has unleashed a barrage of immigration orders and policy changes, including guidance that immigration officers will be allowed conduct enforcement at sensitive locations such as schools and churches.

Ice declined to provide details about the date and location of its raid in New Jersey. Baraka said that among the people detained there was a US military veteran, “who suffered the indignity of having the legitimacy of his military documentation questioned” by officers.

“This egregious act is in plain violation of the fourth amendment of the US constitution, which guarantees ‘the right of the people be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures’,” the mayor said.

Ice has said the agency “may encounter US citizens while conducting field work and may request identification to establish an individual’s identity as was the case during a targeted enforcement operation at a worksite today in Newark”.

The raids, and its effect on people with and without citizenship have drawn outrage and condemnation from several New Jersey lawmakers, including the US representative Bonnie Watson Coleman. “This is a disgrace,” she wrote in a statement. “This is what we expect from two-bit dictators in banana republics.”

LaMonica McIver, another representative, wrote: “Already, Trump’s attacks on immigrant communities are hitting home and we will not back down.”

The New Jersey Alliance for Immigrant Justice has urged residents to attend “know your rights” workshops it is arranging, to help residents understand their legal rights when they encounter immigration enforcement agents.

Advocates and local leaders in cities across the US have been similarly preparing for raids. In Chicago – where more than 50,000 people, mostly from Venezuela, have arrived in the past two years – the mayor Brandon Johnson said he has been working with community groups to educate residents about their rights.