LOS ANGELES — Counter-protesters “forcefully” attacked a pro-Palestinian encampment at UCLA early Wednesday, the university’s chancellor said, and activists clashed with police officers who destroyed their tents at the University of Wisconsin in Madison, part of a series of escalating violence on some college campuses over the war in Gaza.

UCLA administrators and campus police delayed intervening and calling for law enforcement backup in the brawl on the Los Angeles campus, prompting widespread condemnation from Muslim students to the city’s mayor to California Gov. Gavin Newsom.

The counter-protesters, some of whom carried Israeli flags, threw traffic cones and chairs, released pepper spray, and pulled down the barricade surrounding the encampment. University officials said 15 people were injured in the confrontation, including one person who was hospitalized.

The chaotic scenes unfolded Wednesday after police burst into a building occupied by anti-war protesters at Columbia University on Tuesday night, breaking up a demonstration that had paralyzed the school.

Chancellor Gene Block at UCLA said in a statement that “a group of instigators” came on campus Tuesday night to “forcefully attack” the encampment.

After a couple of hours of scuffles, police wearing in helmets and face shields separated the groups. Later Wednesday, pro-Palestinian protesters rebuilt a barricade around their encampment.

Muslim organizations and students blasted university officials and police in a news conference Wednesday, saying they failed to intervene as students in the pro-Palestinian encampment were verbally harassed, pepper sprayed and beaten.

Speakers disputed the university’s account that 15 people were injured and one hospitalized, saying the number of people taken to the hospital was higher. One student described needing to go to the hospital after being hit in the head by an object wielded by counter-protesters.

Several students who spoke during the news conference said they had to rely on each other, not the police, for support as they were attacked, and that many in the pro-Palestinian encampment remained peaceful and did not engage with counter-protesters.

UCLA canceled classes Wednesday.

In Madison, a scrum broke out Wednesday after police with shields removed all but one tent and shoved protesters. Four officers were injured, including a state trooper hit in the head with a skateboard, authorities said. More tents sprang up within hours. More than 30 people were initially detained, but police said only four were charged with battering law enforcement.

Tent encampments of protesters calling on universities to stop doing business with Israel or companies that support the war in Gaza have spread to campuses nationwide in a student movement unlike any other this century. The ensuing police crackdowns echoed actions decades ago against a much larger movement protesting the Vietnam War.

This is all playing out in an election year in the U.S., raising questions about whether young voters — who are critical for Democrats — will back President Joe Biden’s reelection effort, given his staunch support of Israel.

There have been confrontations with law enforcement and more than 1,300 arrests. In rare instances, university officials and protest leaders struck agreements to restrict the disruption to campus life and upcoming commencement ceremonies.

No arrests at UCLA were reported. Officials did not clarify whether the demonstrators were all students.

Block promised the university will conduct a thorough investigation.

“However one feels about the encampment, this attack on our students, faculty and community members was utterly unacceptable,” Block said. “It has shaken our campus to its core.”

Newsom and Los Angeles Mayor Karen Bass both called for accountability of those involved in the melee. A spokesperson for the governor said outside law enforcement was sent to the campus after “unacceptable” delays in the university’s police force response to the clashes.

The nationwide campus demonstrations to protest Israel’s offensive in Gaza began almost two weeks ago at Columbia.

Late Tuesday, New York City police entered Columbia’s campus and cleared a tent encampment, along with Hamilton Hall, which demonstrators had seized about 20 hours earlier.

New York City Mayor Eric Adams blamed “outside agitators” on Wednesday for leading the demonstrations at Columbia.