PHILADELPHIA -- A group chat with "violent, racist and thoroughly disgusting images and messages" that was targeted at black students at the University of Pennsylvania has been linked to three people from Oklahoma, officials said this weekend.

An investigation found no students at the Ivy League college in Philadelphia were involved in the incident.

Black freshmen at the university were added to an account on the mobile messaging app GroupMe starting on Friday that included pictures of lynching, racist slurs and an event invitation for a "daily lynching." The chats also included references to President-elect Donald Trump, a graduate of the university's Wharton School of Business.

As of Friday, The Associated Press and local news outlets had identified more than 20 incidents of racist incidents at schools and universities across the country since Trump's election. In an interview on CBS's "60 Minutes" that aired Sunday night, Trump delivered a message to any of his supporters accused of inciting violence or using racist slurs: "Stop it."

One of the three people involved in sending the racist messages is a student at the University of Oklahoma, officials said. University of Oklahoma President David L. Boren issued a statement on Friday night condemning the attack and saying that that the university had determined from a "preliminary inquiry that there's a basis for a temporary suspension of the student under our student code while we continue to gather all of the facts."

That suspension was effective immediately, Boren said, adding that it appeared the racists messages "did not originate at the University of Oklahoma."

One student at the University of Pennsylvania said she was "petrified" by the messages.

Black students throughout @Penn's campus, like myself, have been added to this hateful GroupMe. I am petrified and all I want to do is cry. pic.twitter.com/DrqLvpXAW5 — Chidera (@_chidera__) November 11, 2016

Another student wrote on Facebook, "I just can't stop crying. I feel sick to my stomach. I don't feel safe."

University of Pennsylvania President Amy Gutmann on Sunday issued a statement saying that university police were still working with the FBI, as well as law enforcement officials in Oklahoma, and "our hope is that the full investigation into this terrible incident will be concluded shortly."

The statement also said that the criminal investigation had found that no Penn students were involved and the three individuals linked to the racist messages, including the University of Oklahoma student, were all from Oklahoma.

"Our primary concern remains with the students who were the recipients of this dreadful hatred," the statement said. "Many Penn staff members are working with them to be sure that they are receiving all the support that they need."

Erin O'Neill may be reached at eoneill@njadvancemedia.com. Follow her on Twitter @LedgerErin. Find NJ.com on Facebook.