NEW YORK — Dozens of protesters took over a building at Columbia University on Tuesday, barricading entrances and unfurling a Palestinian flag from a window in an escalation of demonstrations against the Israel-Hamas war on college campuses nationwide. The school promised they would face expulsion.

The occupation at the campus in New York — where protesters had shrugged off an earlier ultimatum to abandon a tent encampment Monday or be suspended — unfolded as other universities stepped up efforts to end the protests. Police swept through some campuses, leading to confrontations and arrests. In rarer instances, university officials and protest leaders struck agreements to restrict the disruption to campus life.

And in the Mideast as cease-fire negotiations appeared to gain steam Tuesday, it wasn’t clear whether those talks would inspire campus protesters to ease their efforts.

Protesters on Columbia’s Manhattan campus locked arms in front of Hamilton Hall early Tuesday and carried furniture and metal barricades to the building, among several occupied in a 1968 civil rights and anti-Vietnam War protest.

Posts on an Instagram page for protest organizers shortly after midnight urged people to protect the encampment and join them at Hamilton Hall. A “Free Palestine” banner hung from a window.

“An autonomous group reclaimed Hind’s Hall, previously known as ‘Hamilton Hall,’ in honor of Hind Rajab, a martyr murdered at the hands of the genocidal Israeli state at the age of six years old,” CU Apartheid Divest posted on the social platform X early Tuesday.

The takeover occurred nearly 12 hours after Monday’s 2 p.m. Eastern time deadline for the protesters to leave a 120-tent encampment of or face suspension.

In a statement Tuesday, Columbia spokesperson Ben Chang said, “Students occupying the building face expulsion.”

Chang said the university had given protesters a chance to leave peacefully and finish the semester, but that those who didn’t agree to the terms from Monday were being suspended — restricted from all academic and recreational spaces, allowed only to enter their residences, and, for seniors, ineligible to graduate.

“Protesters have chosen to escalate to an untenable situation — vandalizing property, breaking doors and windows, and blockading entrances — and we are following through with the consequences we outlined yesterday,” he said.

The public safety department said in a statement that access to the campus was limited to students living in the residential buildings and essential employees. There was just one access point into and out of campus.

Protesters have insisted they will remain at the hall until the university agrees to three demands: divestment, financial transparency and amnesty.

The standoffs across the country have drawn concern from the White House. National Security Council spokesperson John Kirby said President Joe Biden believes students occupying an academic building is “absolutely the wrong approach,” and “not an example of peaceful protest.”

At California State Polytechnic University at Humboldt, where protesters occupied two buildings, dozens of police officers in helmets and carrying batons cleared both halls overnight. The school said 25 were arrested. The sweep was aired on KAEF-TV’s Facebook page until police detained the reporter.

At Virginia Commonwealth University in Richmond, police and demonstrators clashed Monday night as officers took down tents, charged the line of demonstrators, deployed chemical agents to disperse the crowd and made arrests, the Richmond Times-Dispatch reported.

Yale said authorities Tuesday morning cleared an encampment after protesters heeded final warnings to leave.