U.S. President Donald Trump vowed a new crackdown Monday on pro-Palestinian protesters on American college campuses, saying the detention of Mahmoud Khalil, a demonstration leader at Columbia University in New York, is "the first arrest of many to come."

"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 U.S. leader said on his Truth Social platform.

Khalil was arrested by U.S. immigration officials over the weekend. He was one of the most prominent figures during the protest movement that erupted at Columbia and some other campuses a year ago in opposition to Israel's war in Gaza against the U.S.-designated terror group Hamas.

But for the most part, the protests died down and did not resume when the new school year opened last fall.

The Department of Homeland Security said Khalil’s arrest was taken "in support of President Trump's executive orders prohibiting anti-Semitism, and in coordination with the Department of State."

Khalil, listed as a Syrian on his detention papers, earned a master’s degree from Columbia’s school of international affairs last semester. He held a permanent U.S. residency green card at the time of his arrest, according to the Student Workers of Columbia union, and is married to an American citizen who is eight months pregnant.

He has not been charged with any criminal offenses.

Trump wrote in a social media posting, “If you support terrorism, including the slaughtering of innocent men, women, and children, your presence is contrary to our national and foreign policy interests, and you are not welcome here. We expect every one of America’s Colleges and Universities to comply.”

The pro-Palestinian protests a year ago disrupted classes at some U.S. campuses following Hamas’ October 7, 2023, terror attack on southern Israel that killed 1,200 people and led to the capture of about 250 hostages, with about two dozen of them still being held in Gaza by the terror group or its affiliates.

Israel’s counteroffensive in Gaza has killed more than 48,000 Palestinians, most of them women and children, according to Gaza health officials. The Israeli military said the death toll includes 17,000 Hamas terrorists.

The campus demonstrations ignited accusations of anti-Semitism. The protests — some of which turned violent with the demonstrators occupying campus buildings and disrupting classes — pitted students protesting Israel's conduct against pro-Israel campaigners, many of whom were Jewish.

Khalil’s lawyer said the agents who arrested him Saturday at his university-owned home near Columbia said they were revoking his green card. He is being held in an immigration detention center in the Southern state of Louisiana.

The Council on American-Islamic Relations, a national Muslim civil rights advocacy group, said Monday it is working with Khalil's lawyer and called for his immediate release.

Khalil "is a lawful permanent resident of our nation who has not been charged with or convicted of a single crime," the Washington-based group said in a statement. "The Department of Homeland Security's lawless decision to arrest him solely because of his peaceful anti-genocide activism represents a blatant attack on the First Amendment's guarantee of free speech, immigration laws, and the very humanity of Palestinians."

Secretary of State Marco Rubio said in a message posted Sunday on X that the administration will be "revoking the visas and/or green cards of Hamas supporters in America so they can be deported." Khalil’s arrest is the first publicly known deportation effort linked to the Palestinian protests since the Trump administration took office in January.

At the time of the protests a year ago, Khalil and other student leaders of the Columbia University Apartheid Divest student group rejected claims of antisemitism, saying they were part of a broader anti-war movement that included Jewish students and other groups.

But the divestment group has also expressed support for leaders of both Hamas and Hezbollah, another Islamist organization chiefly in Lebanon that the U.S. has also designated as a terrorist group.

It is unclear when Khalil will have a hearing in an immigration court, which is typically the first step in the deportation process.

Khalil was one of the most visible activists in last year's protests at Columbia, serving as a negotiator for students who erected a tent encampment on campus. Pro-Israel activists in recent weeks have called on the Trump administration to begin deportation proceedings against him.

A new Columbia office that has already brought disciplinary charges against dozens of students for their pro-Palestinian protests has also opened an investigation of Khalil.

The Trump administration last week revoked $400 million in federal funding from Columbia because of what it claimed was the Ivy League school's failure to reign in antisemitism on campus.

Some material in this report came from Agence France-Presse and The Associated Press.