While it is unclear when the threats began, or even if there were any to begin with, schools moved cautiously in response, in some cases sending emails to concerned parents about how they are handling the situation. 

Gilroy High School in Gilroy, Calif., canceled classes on Friday, a decision that the superintendent said was “not an easy one” as students were preparing to take their final exams before the holiday break. Some districts in Texas, Minnesota, and Missouri also canceled their classes, according to reports. 

Meanwhile, in Arizona, Connecticut, Illinois, Montana, New York, and Pennsylvania, school officials increased police presence on school campuses Thursday, according to the Associated Press. 

So far, school leaders and government officials have said they have found no posts on TikTok discussing specific threats, and that there is little evidence to show that the rumors of violence are credible. Most posts merely discuss worries about attacks on schools rather than air actual threats.  

New Jersey Gov. Phil Murphy addressed the “viral social media school threats,” yesterday on Twitter, stating that “there are no known specific threats against New Jersey schools.”

The Department of Homeland Security tweeted today that it “does not have any information indicating any specific, credible threats to schools but recommends communities remain alert.”

The New York Police Department also released a bulletin stating that it was “aware of social media posts circulating on TikTok concerning a potential school shooting on Friday, December 17th.”

“At this time, [NYPD] would like our public and private sector security members to know there is no credible information to suggest this threat is specific to any school in New York City,” the bulletin read. “Out of an abundance of precaution, the NYPD has deployed extra resources around city schools.”

Although TikTok has said it is working with law enforcement to investigate the matter, the company said there was no proof that any threats of gun violence originated on its platform, or even gained traction there.

“We handle even rumored threats with utmost seriousness, which is why we’re working with law enforcement to look into warnings about potential violence at schools even though we have not found evidence of such threats originating or spreading via TikTok,” the social media giant wrote on its Twitter Wednesday. 

TikTok did not respond to Fortune’s request for additional comment about the threats specifically, but it did criticize media outlets for airing the rumors. The service suggested that reporting on the rumors could increase the likelihood of violence.  

“Our employees, who are also parents and members of the community, share the worry that families and educators across the country are feeling based on media reports that content rumored to be on TikTok could promote school violence,” a spokesperson from TikTok told Fortune. “We continue to aggressively search for any such content on our platform, but we are deeply concerned that the proliferation of local media reports on an alleged trend that has not been found on the platform could end up inspiring real-world harm.”

The rumors come just two weeks after four students were killed and several others severely injured after a shooting at an Oxford, Mich., high school. After that attack, many parents took to Twitter to express frustration about having to fear for their childrens’ lives when sending them to school.