There was an explosion early Saturday at Harvard University’s medical school that appears to have been intentional, but no one was injured, authorities said.

Police at the Massachusetts Ivy League university said in a statement that an officer who responded to a fire alarm encountered two unidentified people and tried to stop them. But they ran from the campus’s Goldenson building before the officer got to where the alert was triggered by an explosion, police said.

The Boston fire department determined that the explosion was intentional. 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.