Protesters in New York and rights groups expressed outrage on Monday over the arrest of a leader of pro-Palestinian demonstrations at Columbia University, as President Donald Trump vowed further crackdowns.

Mahmoud Khalil, a recent graduate and one of the most prominent faces of the university's high-profile protests, was arrested by US immigration officials over the weekend despite holding a permanent residency green card.

The Department of Homeland Security, confirming Khalil's arrest on Sunday, claimed he had "led activities aligned to Hamas" and that the DHS action was taken "in coordination with the Department of State."

"We know there are more students at Columbia and other Universities across the Country who have engaged in pro-terrorist, anti-Semitic, anti-American activity, and the Trump Administration will not tolerate it," the president wrote on Monday on his Truth Social platform.

"This is the first arrest of many to come," he pledged.

The protests at Columbia, launched last year in opposition to Israel's devastating war in Gaza, brought widespread media attention as tensions mounted on campus and spread to other universities around the country.

Trump and other Republicans have broadly accused the protesters of supporting Hamas.

While the Trump administration moves to quickly deport Khalil, who has reportedly been moved to the southern state of Louisiana, a federal judge on Monday ordered authorities to halt proceedings.

The American Civil Liberties Union (ACLU) condemned Khalil's arrest, calling it "unprecedented, illegal, and un-American."

"The government's actions are obviously intended to intimidate and chill speech on one side of a public debate," said Ben Wizner, director of the ACLU's Speech, Privacy and Technology Project, in a statement.

On Monday afternoon, over 1,000 protesters gathered in New York to express their outrage at Khalil's arrest.

"This was essentially a kidnapping," said 42-year-old Tobi, who declined to give her last name for fear of retaliation.

"It seems like a clear targeting of activists, which is a really, really dangerous precedent," she said. (AFP)