Denver’s East High School was one of several Colorado schools to receive hoax calls about active shooters Monday, terrifying thousands of students and parents from the San Luis Valley to Colorado Springs.

An FBI spokesperson said Monday that the agency is aware of “numerous swatting incidents” where hoax callers reported active shooters at Colorado schools, hoping to elicit SWAT responses. Law enforcement in Virginia, meanwhile, responded Monday to false threats at several schools around the state.

Around 1:53 p.m., police received a call of an active shooter at East High from a male caller, who said they were a teacher and provided a suspect description and the school address before hanging up, Denver police Chief Ron Thomas said during an afternoon news conference.

Officers arrived at East High in less than two minutes, Thomas said, while authorities searched the school’s camera system to determine if there was a threat.

“There was no indication of a shooting,” Thomas said.

The acting chief said police believe the call came from outside the building and not from a teacher. Authorities are not sure whether the hoax was connected to any other calls around the state.

A large police presence could be seen outside East High on Monday afternoon as dozens of teens were being escorted out of school, walking calmly.

The district, around 4 p.m., said the school has been deemed safe and students would be dismissed. All after-school practices and activities were canceled.

One young person was seen in handcuffs being escorted away from the school by a police officer, an incident Thomas said was unrelated.

Steve Katsaros, whose 15-year-old son is a sophomore at East, said a faculty member texted him a picture of SWAT cars in front of the school.

“What parent wouldn’t lose their (expletive),” he said.

Katsaros expressed disappointment in school and district administration for what he said was a lack of information about Monday’s incident.

The large police presence comes just days after authorities arrested two teens in connection with a double shooting on East Colfax Avenue, just around the corner from East High.

Police said a fight broke out Sept. 7 between the two teens and an adult man before one of the suspects fired a weapon. The adult, 20, and an uninvolved juvenile bystander were hit by the gunfire and taken to the hospital.

There were at least two other fake threats on Monday around the state.

Colorado Springs police said on Twitter that they received a call around 2:30 p.m. about an active shooter at an area school. “It was quickly determined that this was a swatting call,” police said.

Around the same time, schools in Alamosa went on lockdown after a caller made a similar threat, the Valley Courier newspaper reported.

Schools officials there said that a 911 call from an administrative number did not actually originate from the district, the paper reported. Officials there blamed the call on “swatting.”

Vikki Migoya, an FBI spokesperson, confirmed that the agency is working with local law enforcement on some of these regional incidents.

“The FBI takes swatting very seriously because it puts innocent people at risk and drains law enforcement resources,” she said in a statement.

Across the country, police responded en masse to multiple Virginia-area schools on Monday for similar calls, local news outlets reported.

A string of false alarms at Houston-area high schools last week prompted the FBI to say it is “aware of numerous swatting incidents” in which callers reported active shooters or bomb threats.