LOS ANGELES — Counter-protesters “forcefully attacked” a pro-Palestinian encampment at the University of California, Los Angeles, early Wednesday, 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.

Fifteen people were injured during the UCLA confrontation, including one person who was hospitalized, according to the president of the University of California system. 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 to “forcefully attack” the pro-Palestinian encampment, prompting the school to ask for assistance from outside law enforcement.

After a couple of hours of scuffles between dueling demonstrators at the University of California, Los Angeles, police wearing helmets and face shields separated the groups and restored calm. Later Wednesday, pro-Palestinian protesters rebuilt a barricade around their encampment. There were no counter-protesters in sight, and law enforcement officers were deployed throughout the campus.

In Madison on Wednesday, police with shields removed all but one tent and shoved protesters, resulting in a scrum. Four officers were injured, including a state trooper who was hit in the head with a skateboard, according to University of Wisconsin police spokesperson Marc Lovicott.

Within hours, protesters had erected more tents at the UW campus.

More than 30 people were arrested, most of them released without charges, but four were charged with battering law enforcement, police said.

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

The clashes at UCLA erupted when the pro-Palestinian protesters tried to expand their encampment late Tuesday night. Counter-protesters then tried to pull down the parade barricades, plywood and wooden pallets surrounding the encampment. In the chaos, firecrackers exploded.

Police left the scene around 11:30 p.m., and police in riot gear showed up at 1:45 a.m. to establish a perimeter. Counter-protesters, a few of whom were carrying Israeli flags, threw traffic cones and chairs, released pepper spray, and tore down barriers around the encampment. Some from the pro-Palestinian camp hopped over the barriers and scuffled with the counter-protesters.

No one was arrested. Officials have not clarified whether the demonstrators were all students.

Chancellor Block offered his sympathy to those who were injured and anyone who feels unsafe on campus, and promised the university will conduct a thorough investigation that he said may lead to arrests, expulsions and dismissals. In addition, Block said the administration is examining its own security response.

“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 and — adding to other abhorrent incidents that we have witnessed and that have circulated on social media over the past several days — further damaged our community’s sense of security.”