Harvard University Police and the FBI are searching for two suspects linked to an explosion at Harvard Medical School early Saturday morning.

The incident occurred just before 3 a.m. in the fourth-floor hallway of the Goldenson Building on Longwood Avenue in Boston.

No one was injured, and a Harvard police officer saw two people fleeing the scene.

Harvard released grainy images of the suspects, who wore sweatshirts and had their faces covered.

The Boston Fire Department described the explosion as “appeared to be intentional,” but no other devices were found and there was no structural damage; all labs and equipment remain intact.

Harvard police said there is no ongoing public safety threat, and classes resumed Monday.

Patrols on campus have been increased, CBS News has reported.

Anyone with information is urged to contact Harvard University Police’s detective bureau.