Police officers secure an area at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013. Four buildings on campus were evacuated after campus
Police officers secure an area at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013. Four buildings on campus were evacuated after campus police received an unconfirmed report that explosives may have been placed inside, interrupting final exams. (AP Photo/Josh Reynolds) (Josh Reynolds)

CAMBRIDGE, Mass. (AP) -- Harvard University has issued an all-clear for two of the four campus buildings evacuated because of a report of possible explosives.

Students have been told that they can return to Thayer Hall, which is a dorm, and Emerson Hall, a classroom building.

The two other buildings, the Science Center and another classroom building, remain closed. A search has yet to turn up any explosives.

An alert went out just after 9 a.m. Monday telling students at the Ivy League school outside Boston to leave the four buildings.

It's exam time at Harvard and some students were just about to start finals when the alert went out.

The FBI is investigating along with Cambridge and university police and other agencies.

A police officer secures an area at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013. Four buildings on campus were evacuated after campus
A police officer secures an area at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013. Four buildings on campus were evacuated after campus police received an unconfirmed report that explosives may have been placed inside, interrupting final exams. (AP Photo/Josh Reynolds) (Josh Reynolds)


A security officer guards a gate and keeps people from Harvard Yard at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013. Four buildings on
A security officer guards a gate and keeps people from Harvard Yard at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013. Four buildings on campus were evacuated Monday after campus police received an unconfirmed report that explosives may have been placed inside, interrupting final exams. (AP Photo/Elise Amendola) (Elise Amendola)

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