Campus police officers at the University of Arizona in Tucson shot "chemical irritant" munitions at a gathering of protesters early Wednesday, the department said.

The university's president, Robert C. Robbins, had asked the campus police and school officials to "immediately enforce campus use policies and all corresponding laws," according to a statement from his office.

The Tucson Police Department and other law enforcement agencies also responded to campus, the university said.

Campus officers closed several blocks of Park Avenue as they responded to the "unlawful assembly," the department said.

Video appeared to show police handcuffing individuals on the ground and protesters forming a human chain facing officers.

"Police deploying chemical irritant munitions," the department said amid a series of updates on social media. "Follow orders of police and disperse immediately. Avoid the area of University Blvd & Park Ave."

-ABC News' Amanda Morris and Kevin Shalvey

As groups of counter-protesters clashed with Pro-Palestinian demonstrators on the UCLA campus early Wednesday, a university official said staff were “sickened” by the violence.

“Horrific acts of violence occurred at the encampment tonight and we immediately called law enforcement for mutual aid support,” Mary Osaka, a vice chancellor, said in a statement.

Osaka aded that the fire department and medical responders were near the scene.

"We are sickened by this senseless violence and it must end,” she said.

-ABC News’ Bonnie Mclean and Kevin Shalvey

The New York Police Department made at least 100 arrests overnight, with most at Columbia University. Arrests were also made at City College of New York, officials said.

Many of those taken into custody are still being processed at police headquarters.

-ABC News’ Aaron Katersky

Clashes between opposing groups of protesters at the University of California Los Angeles included "multiple acts of violence," prompting university officials to ask police to enter the campus, the Los Angeles Police Department said.

Officers responded to assist campus police "to restore order and maintain public safety," the LAPD said.

State and local politicians said they were monitoring the situation, with Los Angeles Mayor Karen Bass calling the violence "absolutely abhorrent and inexcusable."

Gov. Gavin Newsom said his office had been in contact with law enforcement leadership.

-ABC News' Bonnie Mclean, Amanda Morris and Kevin Shalvey

In a letter authorizing the NYPD to enter the Columbia University campus and break up the protest, the school detailed the backstory on its recent talks with those in the encampments and the takeover Tuesday night of Hamilton Hall.

According to the letter, from Columbia President Minouche Shafik, an individual "hid in the building" at Hamilton Hall until it was closed and let others in. The group's purpose was "occupying the building," the letter read.

Two security guards were inside the building at the time, and the university said in the letter to the NYPD they were able to "secure their release."

"We believe that while the group who broke into the building includes students, it is led by individuals who are not affiliated with the University," the letter read. "The individuals who have occupied Hamilton Hall have vandalized University property and are trespassing."
Addressing the encampment on the school's Morningside campus, the university told police discussions had been carried out with group representatives, but on Sunday, they "reached an impasse."

At that time, the university says it told the group they did not have permission to "occupy spaces on campus" and were "in violation" of school rules and policies.
On Monday morning, the protesters were told they would be suspended if they didn't disperse by Monday at 2 p.m. ET.

The university said in its Tuesday night NYPD letter that those in the encampment were "suspended" and "not authorized to be on University property and are trespassing."

The university said it believed the actions of those in the protest were escalating. "These activities have become a magnet for protesters outside our gates which creates significant risk to our campus and disrupts the ability of the University to continue normal operations," the letter read.

Columbia's president concluded the letter by asking the NYPD to "help to clear all individuals from Hamilton Hall and all campus encampments."

She further asked police to have a campus presence through May 17 -- graduation is May 15 -- "to maintain order and ensure encampments are not reestablished."

Police moved onto the Columbia University campus a little before 9 p.m. ET and began making arrests.

The NYPD also used a vehicle with an extendable roof ramp to help officers breach Hamilton Hall from an upper floor. From there, the police cleared the building.

The campus encampment and hall were cleared before 11:30 p.m.

-ABC News' Jolie Lash, Aaron Katersky and Joshua Hoyos