Boston: Two Massachusetts men were arrested in connection with a weekend explosion at Harvard Medical School, authorities said.

Logan David Patterson (18) of Plymouth and Dominick Frank Cardoza (20) of Bourne were charged with conspiracy to damage property by means of fire or an explosive, according to federal prosecutors. Both were arrested Tuesday morning and were to be arraigned in federal court later in the day.

The explosion occurred early Saturday on the fourth floor of the Goldenson Building, which houses labs and offices linked to Harvard's neurobiology department. No injuries were reported.

US Attorney Leah B. Foley said at a news conference that public anxiety naturally increases after such incidents, especially in Boston, but assured there was no ongoing threat to the university.

The charging documents stated that surveillance footage showed Patterson and Cardoza walking toward the medical school after attending Halloween events at Wentworth College. Witnesses told investigators the men chose the building because it appeared abandoned and accessed it through the roof.

Harvard officials confirmed that the blast caused no structural damage and that labs and equipment remained intact. The Boston Fire Department ruled the explosion intentional, though no additional devices were found during police sweeps.

An officer responding to a fire alarm had seen two people running from the building shortly after the explosion, university police said.