BOSTON — There was an explosion early Saturday at Harvard Medical School that appears to have been intentional, but no one was injured, authorities said.

A university police officer who responded to a fire alarm tried to stop two unidentified people who ran from the Goldenson Building before going to where the alert was triggered, university police said in a statement.

The Boston Fire Department determined that the explosion was intentional and officers did not find additional devices in a sweep of the building, police said.

Police released grainy photos of two people wearing face coverings and what looked like sweatshirts.