Updated

Ohio State University reopened two labs Tuesday night that were targeted in a bomb threat that prompted the school to close four buildings, including the main library, and three streets, disrupting campus life for hundreds of students, staff and faculty.

The library and a third lab were scheduled to reopen later Tuesday. No bombs were found in the two buildings that were reopened, and an earlier search of all four turned up nothing out of the ordinary, officials said.

The threat was in a message received Tuesday at FBI headquarters in Washington, said Paul Bresson, a spokesman based there. The bureau had several leads and was continuing to investigate, its Cincinnati spokesman, Michael Brooks, said late Tuesday.

Ohio State is one of the nation's largest universities, with more than 56,000 students at its main Columbus campus. Campus police said they were alerted at 8:19 a.m. Tuesday that the threats involved the William Oxley Thompson Memorial Library and three laboratory buildings.

Authorities did not identify the source of the bomb threats. Bresson declined to provide information about where the e-mail appeared to come from or whether the FBI believed the threat was real.

University officials did not give details on the nature of the threats and declined to speculate on why the four buildings were targeted.

"It's a little worrisome. Maybe there won't be a warning next time," said Todd Elder, 21, a psychology major from Columbus.

Staff members outside one of the labs had thought they were being evacuated for a routine fire drill. Many left purses, coats and car keys in their offices and were stuck waiting for hours in the cold rain as investigators went through the buildings with bomb-sniffing dogs.

Art history professor E. Okechukwu Odita was stranded because his car was parked behind police tape.

"I appreciate what they are doing. We don't want the whole place to blow up," Odita said as he waited on a bench near the labs.

Students and faculty members were warned by text-message alerts and online and phone messages to stay clear of the buildings through the afternoon, said Bob Armstrong, the head of university emergency management. Some students complained they received alerts more than an hour after they were sent.

Public Safety director Vernon Baisden said he could not specify how many students were affected by the evacuations.

Baisden said other classes and functions on campus continued as scheduled, though some students said instructors had called off some classes in buildings near the evacuated labs and library.

The Thompson library sits at the head of the campus' central green, The Oval. Also affected were McPherson Chemical Lab, which houses the chemistry and astronomy departments; Smith Laboratory, which houses engineering experiments and anthropology; and Scott Laboratory, a mechanical engineering building.

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Associated Press writers Dan Sewell and Lisa Cornwell in Cincinnati and Pete Yost in Washington contributed to this report.