Authorities are investigating an early morning explosion deemed “intentional” at Harvard Medical School’s Goldenson Building in Boston on Saturday. No injuries were reported, but officials said two unidentified individuals were seen fleeing from the building shortly after the incident.

The Harvard University Police Department (HUPD) said a fire alarm went off at 2:48 a.m. inside the Goldenson Building, part of Harvard’s Longwood Medical Area. A responding officer saw two individuals running from the scene and attempted to stop them before proceeding inside. The explosion was later determined to have occurred on the building’s fourth floor.

Steven G. Catalano, a spokesperson for the HUPD, said the Boston Fire Department’s arson unit assessed the blast and concluded it was “intentional.” The Boston Police Department conducted a full sweep of the building for additional explosive devices but found none.

Local, state, and federal authorities—including the FBI’s Boston Field Office—are assisting in the ongoing investigation. FBI spokesperson Kristen M. Setera described the investigation as “very active” and confirmed that agents remain on-site to support evidence collection and coordination among agencies.

Harvard University released surveillance images Saturday afternoon of two individuals captured near the Goldenson Building. One suspect was seen wearing khaki pants, gray Crocs, and a brown hooded sweatshirt with the letters “NYC” printed on it. The other was dressed in dark plaid pajama pants and a dark hooded sweatshirt. Both individuals had light-colored ski masks covering their faces. The university urged anyone with information to contact the HUPD.

Authorities have not yet provided details on the extent of the damage to the Goldenson Building, which dates back to 1906 and houses portions of the Department of Neurobiology. The structure is part of Harvard’s extensive network of research and laboratory facilities within the Longwood Medical Area. Faculty was advised to avoid the area unless necessary, noting that only part of the building remains closed.

The Boston Fire Department did not immediately comment on the cause or materials involved in the explosion. Officials have not disclosed whether any flammable or hazardous laboratory substances were affected. No motive has been identified, and authorities have not confirmed whether the suspects have any known connection to the university.

The explosion comes as Harvard University faces heightened public scrutiny following recent federal funding disputes with the Trump administration. However, investigators have not drawn any link between those developments and the incident at the medical school.

As of Sunday, investigators were still working to identify the two individuals and determine what led to the explosion. University officials emphasized their cooperation with law enforcement and said safety remained their top priority for students, faculty, and staff.