Police used tear gas to disperse pro-Palestinian protesters at the University of Arizona Tucson campus early Friday morning after they refused to leave their encampment, according to numerous reports.

The school said, “A structure made from wooden pallets and other debris was erected on campus property after 5 p.m. in violation of the policy. University officials issued warnings to remove the encampment and disperse. The warnings were ignored” despite the school’s president, Robert C. Robbins, instituting “a zero-tolerance approach to enforcing its campus.”

According to the statement, police vehicles were spiked and rocks and water bottles were thrown at officers and university staff. “Those who have violated the law are subject to arrest and prosecution,” the statement continued.

CBS Tucson affiliate KOLD-TV said it confirmed that bottles were being tossed.

The Arizona Daily Star posted video of what happened nect:

KOLD reports that a large group of law enforcement moved in on the demonstrators shortly after midnight local time “after they ignored several commands to disperse. The officers used gas and tore down” the encampment, which had been fortified with wood and plastic barriers.”

KOLD says the protesters then left the campus and moved across the street before police fired more gas at them. They then left the area.

The school said the decision to use law enforcement was made “to ensure the safety of … attendees” of the commencement ceremony scheduled for Friday night.