Harvard University sounds all clear, no bombs found after threat

Harvard University said on Monday that a search of four campus buildings targeted by an "unconfirmed" bomb threat had turned up no explosives and that the buildings had reopened for normal business.

"Nothing to substantiate the emailed threat has been found and the investigation regarding the source is ongoing," the Ivy League school, located in Cambridge, Massachusetts, just outside Boston, said on its website.

Three classroom buildings - The Science Center, Sever and Emerson Halls - and one dormitory, Thayer Hall, were affected, Harvard said.

The threat comes three days after coordinated attacks by gunmen and suicide bombers killed 129 people in Paris.