(NewsNation) — A spate of hoax calls about active shooters on U.S. college campuses is causing anxiety among students as the school year begins.

The calls have prompted universities to issue campuswide texts to “run, hide, fight.” Students and teachers have rushed to find cover, often cowering in classrooms for safety. Officers have swarmed campuses seeking out the falsified threats.

The hoax calls and false alarms have hit at least 11 college campuses from Arkansas to Pennsylvania.

On Monday alone, law enforcement responded to calls claiming there were active shooters at Arkansas, Northern Arizona University, Iowa State, Kansas State, Colorado University and the University of New Hampshire. More calls were made Tuesday at the University of Kentucky as well as Central Georgia Technical College and a nearby high school. The Kentucky call was determined to be a hoax before an alert could be issued.

The FBI said Tuesday that it was working with law enforcement on the swatting cases on college campuses.

We are aware of recent swatting incidents involving a number of colleges and universities and are working with our law enforcement partners. The FBI is seeing an increase in swatting events across the country, and we take potential hoax threats very seriously because it puts innocent people at risk. Knowingly providing false information to emergency service agencies about a possible threat to life drains law enforcement resources, costs thousands of dollars, and, most importantly, puts innocent people at risk. We work closely with our law enforcement partners to determine their credibility, share information, and take appropriate investigative action. As always, we encourage members of the public to remain vigilant and immediately report anything they consider suspicious to law enforcement.

– FBI statement to NewsNation

The wave of reports began Thursday, when law enforcement in Pennsylvania received multiple calls about shots purportedly fired on Villanova’s campus by a man armed with an AR-15-style weapon. Sounds of gunfire could be heard in the background of the calls.

Two hours later, the lockdown was lifted, and the school’s president denounced the “cruel hoax.”

The same day, Tennessee authorities received calls reporting an active shooter at the University of Tennessee at Chattanooga armed with an AR-15-style rifle and four people shot. Dispatchers reported hearing multiple gunshots on the calls.

“This incident was a criminal act, intended to be disruptive and cause chaos,” the school said in a statement.

The University of South Carolina also received two calls Sunday reporting an active shooter at the school’s library, with the sound of gunshots in the background.

The Associated Press contributed to this report.