US authorities arrested 538 migrants and deported hundreds in a mass operation just days into President Donald Trump’s second administration, his press secretary said late on Thursday.

“The Trump Administration arrested 538 illegal immigrant criminals,” Karoline Leavitt said in a post on social platform X, adding “hundreds” were deported by military aircraft.

“The largest [mass] deportation operation in history is well underway. Promises made. Promises kept,” she said.

Trump promised a crackdown on illegal immigration during the election campaign and began his second term with a flurry of executive actions aimed at overhauling entry to the United States.

On Thursday Newark city mayor Ras J Baraka said in a statement that Immigration and Customs Enforcement (ICE) agents “raided a local establishment… detaining undocumented residents as well as citizens, without producing a warrant”.

The mayor said one of those detained during the raid was a US military veteran, “this egregious act is in plain violation” of the US Constitution.

An ICE post on X said: “Enforcement update … 538 arrests, 373 detainers lodged”.

New Jersey Democratic Senators Cory Booker and Andy Kim said they were “deeply concerned” about the Newark raid by immigration agents.

“Actions like this one sow fear in all of our communities — and our broken immigration system requires solutions, not fear tactics,” they said in a joint statement.

Trump has vowed to carry out “the largest deportation operation in American history,” impacting an estimated 11 million undocumented migrants in the United States.

On his first day in office he signed orders declaring a “national emergency” at the southern border and announced the deployment of more troops to the area while vowing to deport “criminal aliens.”

His administration said it would also reinstate a “Remain in Mexico” policy that prevailed during Trump’s first presidency, under which people who apply to enter the United States from Mexico must remain there until their application has been decided.

The White House has also halted an asylum program for people fleeing authoritarian regimes in Central and South America, leaving thousands of people stranded on the Mexican side of the border.

Earlier in the week the Republican-led US Congress green-lit a bill to expand pretrial incarceration for foreign criminal suspects.

Trump frequently invoked dark imagery about how illegal migration was “poisoning the blood” of the nation, words that were seized upon by opponents as reminiscent of Nazi Germany.