[Updated at 1:51 p.m. ET] No explosives were found at two U.S. universities that had ordered evacuations after they received bomb threats Friday morning, officials said.

The evacuations happened at the University of Texas at Austin and North Dakota State University. People were allowed back into the University of Texas buildings at noon CT Friday, though Friday's classes have been canceled, the school said on its website.

Police and federal authorities, including a bomb squad, investigated the Texas threats. A University of Texas police spokesman told CNN that "it was a general bomb threat on campus." A university spokeswoman told CNN affiliate KXAN that a male claiming to be with al Qaeda called the university and said that bombs were placed all over campus, and that they would go off at about 10 a.m. CT (11 a.m. ET).

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About 51,000 students attend the flagship university, which is located in central Texas. University spokeswoman Rhonda Weldon said that at any time up to 70,000 people could be on campus.

North Dakota State University told its students and employees to leave campus entirely by 10:15 a.m. CT, according to its website. A NDSU official later said that the campus had been swept, and classes would resume at 2 p.m. CT.