The Trump administration has revoked visas for more than 300 international students across the United States, a move confirmed by universities and U.S. Secretary of State Marco Rubio as part of a nationwide effort targeting foreign students.

"Maybe more than 300 at this point. We do it every day. Every time I find one of these lunatics, I take away their visas," Rubio said during a press conference in Guyana on March 27.

Over the weekend, the visa revocations were reported by dozens of universities nationwide, including prestigious ones like Columbia, Cornell, Harvard and Stanford.

Many affected students had participated in pro-Palestinian campus protests. But university officials said that others with no connection to protests had also suffered visa revocations without explanation.

At Tufts University, Turkish doctoral student Rumeysa Ozturk was arrested by masked immigration agents on March 25 while walking near her home. Video of the arrest showed plainclothes officers taking the 30-year-old into custody as she was heading to break her Ramadan fast with friends, according to her attorney.

The Department of Homeland Security claimed Ozturk "engaged in activities in support of Hamas," though they provided no evidence for this allegation. Ozturk co-authored an opinion piece in the student newspaper criticizing Tufts' response to the Israel-Gaza conflict.

The Turkish embassy said it was working with U.S. authorities regarding Ozturk's detention. "Every effort is being made to provide the necessary consular services and legal support to protect the rights of our citizen," the embassy stated.

At Columbia University, graduate student Mahmoud Khalil, who has legal permanent residency, was detained by immigration authorities last month.

Khalil said in his Columbia Daily Spectator opinion piece that the school "laid the groundwork for my abduction" and urged the students not to "abdicate their responsibility to resist repression."

"Since my abduction on March 8, the intimidation and kidnapping of international students who stand for Palestine has only accelerated," Khalil wrote in Friday's piece.

The actions extend beyond East Coast schools. The University of Colorado and Colorado State University reported a combined total of 10 students with revoked visas this weekend. Meanwhile, Minnesota State University identified five students whose visas were canceled for unclear reasons.

In California, the situation is equally concerning so far.

University of California, Los Angeles reported nine affected international students, while UC Berkeley confirmed six visa revocations -- four for current students and two for recent graduates.

UC Davis officials stated seven students and five recent graduates had their visas terminated, and Stanford University confirmed six visa revocations.

"The federal government has not explained the reasons behind these terminations," UC Davis said in a statement as reported by NBC News.

Universities are scrambling to support affected students.

"We are focused on supporting the success of all of our students, including international students. Each one of our students is seeking to advance their careers and the lives of their families, and we understand the anxieties that visa revocations cause to impacted students," reported NBC News, citing University of Colorado.

The Council of University of California Faculty Associations issued a statement Sunday, urgently calling upon the University of California to address the revocation of visas and deportation of international students.

"It has been reported that in the past week alone, at least 44 students across the UC system have had their I-20 Student and Exchange Visitor Information System record terminated by the Department of Homeland Security, with at least one deportation occurring," the statement noted.

Civil rights organizations have condemned the administration's actions. The American Civil Liberties Union issued an open letter to universities warning: "The federal government cannot mandate student expulsions or threaten funding cuts to suppress constitutionally protected speech."

College officials worry this crackdown will deter international students from studying in the United States in the future.

The situation is "a far different, unprecedented intrusion by the executive branch" involving "revoking student visas for different reasons than we have seen previously and at higher rates than we have ever seen," said Violeta Chapin, a University of Colorado Boulder law professor and immigration expert.