Harvard University said on Monday it had evacuated four buildings on its campus outside Boston after receiving an "unconfirmed" bomb threat and that the search would likely take several hours.

Three classroom buildings - The Science Center, Sever and Emerson Halls - and one dormitory, Thayer Hall, were affected, the Ivy League school said on its website.

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