The Trump administration is trying to deport pro-Palestinian students and academics who are legally in the United States, a new front in its clash with elite schools over what it says is their failure to combat antisemitism.

The White House asserts that these moves — many of which involve immigrants with visas and green cards — are necessary because those taken into custody threaten national security. But some legal experts say that the administration is trampling on free speech rights and using lower-level laws to crack down on activism.

Secretary of State Marco Rubio said on Thursday that the State Department under his direction had revoked the visas of more than 300 people and was continuing to revoke visas daily. He did not specify how many of those people had taken part in campus protests or acted to support Palestinians.

Mr. Rubio gave that number at a news conference, after noting that the department had revoked the visa of a Turkish graduate student at Tufts University. He did not give details on the other revocations.

Immigration officials are known to have pursued at least nine people in apparent connection to this effort since the start of March.

The detentions and efforts to deport people who are in the country legally reflect an escalation of the administration’s efforts to restrict immigration, as it also seeks to deport undocumented immigrants en masse.

Here is what we know about the college detentions.

Who is being targeted?

The nine people who have been pursued and, in some cases, detained by federal officials include current and former students and professors. Most of them have publicly expressed pro-Palestinian views. Some have green cards, making them lawful permanent residents. Others have student visas, which allows foreign nationals to enter the United States for full-time study.

The extent of their involvement in pro-Palestinian advocacy varies. Mahmoud Khalil, a lawful permanent resident who is believed to be the first to be taken into custody, helped lead high-profile protests at Columbia University against Israel’s war in Gaza. Mr. Khalil, who has Palestinian heritage, is married to an American citizen who is eight months pregnant. He was sent to a detention center in Louisiana.

The administration has also targeted students who have been less involved. Rumeysa Ozturk, a Turkish citizen and graduate student at Tufts University, was taken into federal custody on Tuesday. She had drawn the attention of a right-wing group that claims to combat antisemitism on college campuses and publicizes its findings online after helping write an opinion piece in the student newspaper criticizing the university’s response to pro-Palestinian demands.

Tricia McLaughlin, a spokeswoman for the Department of Homeland Security, said investigators with that agency and Immigration and Customs Enforcement “found Ozturk engaged in activities in support of Hamas, a foreign terrorist organization that relishes the killing of Americans. A visa is a privilege, not a right.” She did not offer evidence or details of that support.

A video of Ms. Ozturk’s detention, showing plainclothes agents from the Homeland Security Department detaining her as she was heading out to break her Ramadan fast with friends, has circulated widely online. “This video should shake everyone to their core,” her lawyer, Mahsa Khanbabai, said in a statement on Wednesday. Ms. Ozturk is being held in Louisiana.

As it scrutinizes people living in the United States, investigators for ICE have been searching videos, online posts and news clippings of campus protests against the Israel-Hamas war. The government also appears to be getting information from private organizations.

Who else has the government sought to deport?

Several other students and academics have been detained or are being sought.

• Ranjani Srinivasan, a Fulbright recipient from India who was pursuing a doctoral degree in urban planning at Columbia, fled to Canada after immigration authorities revoked her student visa.

• Yunseo Chung, a 21-year-old Columbia student and legal permanent resident from South Korea, has been targeted for deportation by immigration agents. A federal judge ordered the Trump administration on Tuesday to halt its efforts.

• Leqaa Kordia, a Palestinian student from the West Bank who had been involved in the protests at Columbia, was taken into custody by immigration agents after overstaying a student visa that was terminated in 2022.

• Momodou Taal, a dual citizen of Gambia and Britain pursuing a doctorate in Africana studies at Cornell, was ordered to surrender to Immigration and Customs Enforcement. A prominent pro-Palestinian voice on campus, Mr. Taal had previously filed a pre-emptive lawsuit to block possible action against him.

• Badar Khan Suri, an Indian citizen who was studying and teaching at Georgetown University, was detained at his home. He is married to a Palestinian American woman whose father is a former adviser to a deceased Hamas leader. A federal judge has temporarily blocked Mr. Suri’s deportation. He is “awaiting his court date” in Alexandria, La., according to his lawyer.

• Dr. Rasha Alawieh, a kidney transplant specialist and professor at Brown University’s medical school, was deported despite holding a valid visa. She was detained upon returning from a trip abroad to Lebanon, her home country, and expelled in possible defiance of a court order. A lawyer representing a member of Dr. Alawieh’s family has vowed to continue fighting.

• Alireza Doroudi, an Iranian citizen and doctoral student at the University of Alabama, was taken into custody and detained by immigration officials. A Homeland Security official said on Thursday that Mr. Doroudi “posed significant national security concerns” but did not provide additional information about why he was detained.

Are these detentions and deportations legal?

The Trump administration has justified the actions by citing a rarely used provision of the Immigration and Nationality Act of 1952, which grants the secretary of state broad authority to expel foreigners deemed to pose “potentially serious adverse foreign policy consequences” for the United States.

But legal experts question whether the actions of the targeted students meet this threshold. Lawful permanent residents are also protected by the Constitution, including free speech and due process rights, which could set up a major legal challenge. Lawyers for those whose student visas have been revoked have similarly challenged the administration on constitutional grounds.

In some cases, the administration has also cited lower-level offenses to justify deportation efforts. The government has added new accusations against Mr. Khalil, saying that he withheld information about his membership in organizations, including a United Nations agency that helps Palestinian refugees, when applying for permanent residency. One of Mr. Khalil’s lawyers dismissed these new claims as “patently weak.”

Will more students be targeted?

Administration officials have signaled that these detentions and deportations reflect the beginning of a broader crackdown on pro-Palestinian protesters. President Trump called Mr. Khalil’s case the first of “many to come.”

Reporting was contributed by Edward Wong, Zolan Kanno-Youngs, Tyler Pager and Hamed Aleaziz.