At least three Ivy League institutions in the United States– Brown, Cornell and Columbia universities– saw large evacuations and police investigations on Sunday citing bomb threats. According to media reports, at least two schools have declared the threats unfounded.

The three Ivy League institutions sent out an alert to students about the possible threats, while Columbia and Brown cleared that the campus buildings had been evacuated by evening.

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Law enforcement officials in New York‘s Ithaca, where Cornell University is located, cordoned off the center of the campus after receiving calls about bombs being placed in four buildings through the campus.

Columbia University, which is located in New York City, issued an emergency alert to everyone on the campus around 2:30 PM on Sunday after receiving bomb threats. The threats were later dismissed by the university officials.

Rhode Island’s Brown University officials also sent out text alerts to the students on campus about the possibility of explosives being present on ground. The alerts also said that law enforcement officials were probing “multiple buildings on campus involving a bomb threat”, according to the reports from Associated Press.

Later in the evening, the university issued another alert before 6 PM that said students were safe to resume activity on campus.

“Buildings that had been evacuated are now reopened, and university operations have resumed as normal,” the school said in a statement, according to reports from ABC News.

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The threats came two days after a bomb threat at Yale University forced the evacuation of several buildings, as well as nearby businesses in New Haven, Connecticut. Yale’s campus, resumed normal activities Friday evening, roughly five hours after the call was received, according to reports from Associated Press.

As of Sunday evening, law enforcement officials continued to investigate the threats at Cornell and Brown University. According to media reports, no devices have been found so far in either institution and no arrests have been made.