The US president has warned that he will be watching "communist" Zohran Mamdani very carefully

US President Donald Trump has warned that the presumptive Democratic nominee for New York City mayor, Zohran Mamdani, could be arrested if he follows through on his promise to prevent federal officials from enforcing immigration laws in the country's largest city.

Uganda-born Mamdani said in his victory speech after the New York City Democratic mayoral primary on Tuesday that he would "stop masked ICE (Immigration and Customs Enforcement) agents from deporting our neighbors."

"Well then, we will have to arrest him," Trump said when asked by journalists about the New York state lawmaker's pledge later in the day, as he visited the so-called "Alligator Alcatraz" migrant detention center in Florida.

"Look, we do not need a communist in this country, but if we have one, I am going to be watching over him very carefully on behalf of the nation," the president said, referring to Mamdani.

Trump also claimed that "a lot of people are saying he is here illegally. We are going to look at everything."

The president continued his attacks on the Democratic politician after returning to the White House, describing Mamdani as a "total nut job" and threatening to withhold funding for New York City if he does not "do the right thing."

Mamdani responded to Trump's comments in a statement on X, labeling them an "intimidation" attempt that his supporters and him will not accept.

The president threatened him with arrest and deportation "not because I have broken any law, but because I will refuse to let ICE terrorize our city," the 33-year-old argued.

"His statements do not just represent an attack on our democracy but an attempt to send a message to every New Yorker who refuses to hide in the shadows: if you speak up, they will come for you," he said.

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Mamdani has been living in the US since the age of seven and became a naturalized citizen in 2018. He denies being a communist, describing himself as a democratic socialist.