Three Ivy League schools—Columbia, Cornell, and Brown universities—reported receiving bomb threats on Sunday, prompting multiple building evacuations on each campus. It is not known whether the threats are connected, but there were no subsequent reports of detonations or injuries on any campus as of Sunday evening. According to the Columbia Daily Spectator, evacuations of three buildings around 2:30 p.m. were triggered in response to a Twitter user claiming they were armed and had planted “40 IED explosives” around the campus.

“Following an investigation, the threats were deemed not credible by the NYPD,” read a statement from Columbia’s vice president for public safety, sent just over two hours after the threats were received. Brown and Cornell received bomb threats over the phone, according to their respective public safety departments. Both universities were swept and reopened.

On Friday, Yale University evacuated 10 school buildings after threats were made over the phone. It took authorities five hours to investigate the campus before they determined there was “no validity” to the threats. A day later, Miami University and Ohio University also received similar threats and were cleared to resume normal operations shortly afterward.