Multiple law enforcement agencies are investigating what is believed to have been an intentional explosion on the Harvard Medical School campus in Boston early Saturday morning.

A Harvard University Police Department spokesperson says it happened at the Goldenson Building on Longwood Avenue. In a statement, spokesperson Steven Catalano said a HUPD officer responded to the scene just before 3 a.m. when a fire alarm went off and witnessed two unidentified people fleeing the building.

“Upon entering the building, the officer determined that an explosion had occurred in an area on the 4th floor,” said Catalano. “The Boston Fire Department Arson Unit responded and made an initial assessment that the explosion appeared to be intentional.”

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Harvard University Police say they’re working with local, state, and federal law enforcement partners as the investigation into the explosion plays out, and a Boston FBI spokesperson confirmed they are on the scene. No injuries were reported.

This is a developing story.