Several people at Joint Base Andrews in Maryland became ill after a “suspicious package” was opened on Thursday, prompting the evacuation of two buildings, according to a U.S. military spokesperson.

The individuals were treated by base medical staff, found to be in stable condition, and later released.

Officials said first responders determined there was no ongoing threat, and normal operations have since resumed.

CNN reported that the package may have contained an unknown white powder, though this has not been confirmed, Axios has reported.

Military authorities have launched an investigation into the incident.