CHICAGO (AP) — The University of Chicago canceled all classes and activities scheduled for Monday on its main campus following an online threat of gun violence to which the FBI alerted the school.

The university, one of the leading teaching and research institutions in the nation and where President Barack Obama taught law, said in a statement Sunday night that an online threat from an unknown person mentioned the quad, a popular gathering place, and 10 a.m. Monday.

“It was pretty specific in terms of time and place,” university spokesman Jeremy Manier said.

Manier noted Monday morning that the school won’t say anything beyond its statement, though there may be details later. FBI Chicago spokeswoman Joan Hyde provided no further details about the threat except to say that the FBI was investigating the source.

The statement urged faculty, students and non-essential staff to stay away from the Hyde Park campus on Chicago’s South Side through midnight Monday and told students in college housing to stay indoors.

The normally bustling campus was largely quiet Monday morning with few students walking in the surrounding neighborhoods. Chicago Police Department squad cars and a wagon patrolled streets, along with campus security cars. Security staff in yellow jackets stood on campus walkways, including the quad that was mentioned in the threat. The time mentioned in the threat came and went without incident.

The university said the decision to close was taken following “recent tragic events” at other campuses nationwide. On Oct. 1 at Umpqua Community College in Roseburg, Oregon, a gunman opened fire and killed nine people. Other shootings have happened in Arizona and Tennessee.

Rafael Munez headed to work at a student dining hall, where he’s been employed for three years. He said he was a little nervous walking onto campus on Monday, particularly thinking about recent campus shootings.

“My wife didn’t want me to come to work,” he said. “It’s scary … It puts you on your toes.”

Students closed their books, shut down their laptops and hurried home Sunday when the school first alerted people to the threat, according to student body president Tyler Kissinger.

“I work in the campus coffee shop and when people got the notice (announcements and online) they really cleared out of here immediately,” the 21-year-old senior said.

The announcement, which he said was the first time he’s heard of the school closing for any reason besides inclement weather, also was a reminder of what residents in neighborhoods near campus, which is on the South Side of Chicago, live with every day.

“A lot of people on the South Side live in constant fear of gun violence and, in a sense, we are a bit sheltered from that,” he said.

Junchen Feng, who is pursuing a doctorate, said the threat raised his awareness about gun violence in Chicago and beyond.

“For the first time I was thinking about people who live in Syria, Afghanistan, Pakistan … where they live under constant threats of death and violence,” said the student from China, who planned to spend the day at home and in a campus building that was a five-minute walk away. “It’s a mindset that we just don’t we have.”

Manier said the cancellation of classes and activities would affect more than 30,000 people, including undergraduate and graduate students, faculty and staff.

The University of Chicago Medical Center was open to patients and had added security, the university said. The Medical Center has nearly 7,500 staff.

___

Associated Press writer Greg McCune contributed to this report.