New York City Mayor Eric Adams and New York Police Department officials told reporters that protesters at Columbia University were being influenced by outside individuals, part of a movement "globally" to "radicalize young people"

"Students have a right to protest and free speech is the cornerstone of our society. But as our major concern we knew and we saw that there were those who were never concerned about free speech. They were concerned about chaos. It was about external actors hijacking peaceful protests influence students to escalate," Adams said.

"You don't have to be a majority to influence and co-opt an operation," Adams said.

About 300 people were arrested at Columbia University and City College Tuesday night, New York Mayor Eric Adams said Wednesday.

"We are processing the arrests to distinguish between who were actually students and who were not supposed to be on the grounds," Adams said.

"It was led by individuals who are not affiliated with the university. The school needed the NYPD assistance to clear Hamilton Hall at the encampments outside of dual operations on the grounds that took place successfully," Adams said.

Officials said those arrested could be charged with trespassing, criminal mischef and burglary.

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

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