NEW YORK (AP) — President Donald Trump warned Monday that the arrest and possible deportation of a Palestinian activist who helped lead protests at Columbia University will be the first “of many to come” as his administration cracks down on campus demonstrations against Israel and the war in Gaza.

Mahmoud Khalil, a lawful U.S. resident who was a graduate student at Columbia until December, was detained Saturday by federal immigration agents in New York and flown to an immigration jail in Louisiana.

The Department of Homeland Security said Khalil was taken into custody as a result of Trump’s executive orders prohibiting antisemitism. Khalil has not been charged with any crimes over his activities during campus unrest last year at the university.

“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,” Trump wrote in a social media post. “We will find, apprehend, and deport these terrorist sympathizers from our country — never to return again.”

Khalil’s detention drew immediate outrage from civil rights groups and free speech advocates, who accused the administration of using its immigration enforcement powers to squelch criticism of Israel.

“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,” said the Council on American-Islamic Relations, a national Muslim civil rights advocacy group.

Federal immigration authorities also visited a second international student at Columbia on Friday evening and attempted to take her into custody but were not allowed to enter the apartment, according to a union representing the student. The woman has not been identified, and it’s not clear what grounds ICE had for the visit.

The Student Workers of Columbia, a graduate student union representing the woman, said the three agents did not have an arrest warrant and were “rightfully turned away at the door.”

Khalil is the first person known to be detained for deportation under Trump’s promised crackdown on student protests.

Trump has argued that protesters forfeited their rights to remain in the country by supporting the Palestinian group Hamas that controls Gaza. The U.S. has designated Hamas as a terrorist organization.

Khalil and other student leaders of Columbia University Apartheid Divest have rejected claims of antisemitism, saying they are part of a broader anti-war movement that also includes Jewish students and groups. But the protest coalition, at times, has also voiced support for leaders of Hamas and Hezbollah, another Islamist organization designated by the U.S. as a terrorist group.

It’s unclear when Khalil will have a hearing in immigration court, which is typically the first step in the deportation process. Spokespersons for ICE and DHS did not immediately provide details about his case Monday.

Typically, expelling a person who has permanent residency in the U.S. requires a high bar, such as that person being convicted of certain types of crimes.

Khalil, who was born in Syria to Palestinian parents and has an American citizen wife who is eight months pregnant, emerged as one of the most visible activists in the protests at Columbia.

He served as mediator on behalf of both pro-Palestinian activists and Muslim students, a role that put him in direct touch with university leaders and the press — and drew attention from pro-Israel activists, who in recent weeks called on the Trump administration to deport him.

“He was the administrative interfacing person for any pro-Palestine group on campus that has been too scared to talk to the administration,” another student protester, Maryam Alwan, told The Associated Press. “He took a public facing role, and now he’s being targeted for speaking to the media.”

More recently, Khalil faced investigation by a new disciplinary body set up at Columbia University.

The Office of Institutional Equity sent him a letter last month accusing him of potentially violating a new harassment policy by posting a message in a WhatsApp group referencing a “genocidal dean” who moderated a panel with former Israeli Prime Minister Naftali Bennett.

Khalil told the AP last week that he served as a spokesperson for protesters but did not play a leadership role in the group’s decision-making or have anything to do with its social media posts.

“They are alleging that I was the leader of CUAD or the social media person, which is very far from reality,” he said, using the acronym for the group Columbia University Apartheid Divest.

Khalil received a master’s degree from Columbia’s School of International and Public Affairs last semester. He previously graduated from the Lebanese American University in Beirut with a computer science degree and worked at the British Embassy in Beirut’s Syria office, according to his biography on the Society for International Development’s website.

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.”

Columbia University declined to comment on Khalil’s arrest over the weekend and also did not immediately respond Monday.

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

A protest was scheduled for later Monday in front of a federal office building in Manhattan.