Columbia University canceled in-person classes today and new demonstrations broke out on other U.S. college campuses as tensions continue to grow over Israel’s war in Gaza.

Police arrested several dozen protesters at Yale University today morning after officials at the New Haven, Connecticut, school said they defied warnings over the weekend to leave.

And following arrests last week at Columbia, pro-Palestinian demonstrators set up encampments on other campuses around the country, including at the University of Michigan, the Massachusetts Institute of Technology and the University of North Carolina.

The developments came hours before the Monday evening start of the Jewish holiday of Passover.

Last week, police arrested more than 100 pro-Palestinian demonstrators at Columbia who had set up an encampment on the New York City campus.

On Sunday, a rabbi at Columbia sent a WhatsApp message to more than 200 Jewish students, urging them to leave the New York City campus if they did not feel safe.

Columbia President Minouche Shafik said in a note addressed to the school community today that she was “deeply saddened” by what was happening on campus.

“To deescalate the rancor and give us all a chance to consider next steps, I am announcing that all classes will be held virtually on Monday,” Shafik said.

She said faculty and staff should work remotely, when possible, and that students who don’t live on campus should stay away.

Shafik said the Middle East conflict is terrible and that she understands that many are experiencing deep moral distress.

“But we cannot have one group dictate terms and attempt to disrupt important milestones like graduation to advance their point of view,” Shafik wrote.

Over the coming days, a working group of deans, school administrators and faculty will try to find a resolution to the university crisis, noted Shafik, who didn’t say when in-person classes would resume.

Several students at Columbia and Barnard College said they were suspended for taking part in last week’s protests, including Barnard student Isra Hirsi, the daughter of Democratic U.S. Rep. Ilhan Omar.

At Yale, police officers arrested about 45 protesters and charged them with misdemeanor trespassing, said Officer Christian Bruckhart, a New Haven police spokesperson. All were being released on promises to appear in court later, he said.

Protesters set up tents on Beinecke Plaza on Friday and demonstrated over the weekend, calling on Yale to end any investments in defense companies that do business with Israel.

In a statement to the campus community on Sunday, Yale President Peter Salovey said university officials had spoken to the student protesters multiple times about the school’s policies and guidelines, including those regarding speech and allowing access to campus spaces.

“Putting up structures, defying the directives of university officials, staying in campus spaces past allowed times, and other acts that violate university policies and guidelines create safety hazards and impede the work of our university,” he said.

School officials said they spoke with protesters over several hours and gave them until the end of the weekend to leave Beinecke Plaza. The said they again warned protesters this morning and told them that they could face arrest and discipline, including suspension, before police moved in.

A large group of demonstrators regathered after today’s arrests at Yale and blocked a street near campus, said Bruckhart, the police spokesperson. There were no reports of any violence or injuries.

Last week, the University of Southern California took the unusual step of canceling a planned commencement speech by its 2024 valedictorian, who had publicly supported Palestinians. The university cited security concerns in a decision that was praised by some pro-Israel groups but criticized by free-speech advocates.