Columbia University canceled in-person classes Monday and police arrested several dozen protesters at Yale University as tensions on U.S. college campuses continue to grow over the war in the Middle East.

The moves at the two Ivy League schools came hours before the Jewish holiday of Passover was set to begin Monday evening.

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

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

Columbia President Minouche Shafik said in a note addressed to the school community Monday 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, where possible, and that students who didn’t live on campus should stay away.

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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 will 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, a large group of demonstrators re-gathered after Monday’s arrests and blocked a street near campus, said Bruckhart, the police spokesperson. There were no reports of any violence or injuries.