A US official says a deadly explosion at a Southern California office building is being investigated as an intentional act and investigators believe the blast may have come from a package.
One woman was killed and three others were injured by the Tuesday afternoon (local time) explosion at a medical office building in Aliso Viejo, southeast of Los Angeles.
The official said the information was based on a preliminary investigation. Investigators said they hadn't yet located an explosive device and were searching through debris.
The official was briefed on the investigation but wasn't authorised to discuss the matter publicly and spoke to The Associated Press on condition of anonymity.
The Tuesday afternoon blast on the first floor of an Aliso Viejo building in Orange County shattered windows and forced children in a nearby daycare center to be evacuated.
Mary McWilliams of San Clemente tells the Orange County Register that she saw two women with burns stagger out of the building. Fire officials say a third person suffered smoke inhalation.
Orange County sheriff's experts along with FBI, the ATF and other federal agencies are investigating the cause of the blast. Orange County Sheriff's Cmdr.
Dave Sawyer said that the size of the explosion makes it suspicious.