One person was killed Tuesday and three others injured in an explosion in a medical building in Aliso Viejo, California, authorities said.
The explosion blew out walls and windows, heavily damaging the first floor corner of the two-story building and hurling debris outside, said Capt. Tony Bommarito, a spokesman for the Orange County Fire Authority.
Authorities have not found any explosive devices in the area, and Bommarito said there didn't appear to be a gas leak.
FBI spokesman Mike Gifford said there was no initial indication of terrorism.
"We do not know at this time whether this was an intentional detonation of a device or whether it was an accident," said Orange County Sheriff's Department Commander Dave Sawyer, who added that officials are not ruling out anything.
Sawyer said it appears the blast was concentrated in a suite on the first floor of the office building.
The victim, who was killed, and the three survivors were likely close to the explosion, Sawyer said.
He said investigators are interviewing the three survivors.
Two survivors had critical injuries "that were consistent with an explosion, but not necessarily consistent with a bomb," said Carrie Braun, a spokeswoman for the Orange County Sheriff's Department.
The sheriff's department is partnering with the FBI, the Department of Homeland Security, and the Bureau of Alcohol, Tobacco, Firearms and Explosives, who will assist the investigation, Sawyer said.
Bommarito said firefighters responded to a call of an explosion shortly after 1 p.m. local time. About 10 engines and 70 firefighters were dispatched.
There is a daycare and preschool nearby, but Orange County Fire Authority Chief Brian Fennessy said no children were injured and all are accounted for.
Aliso Viejo is about 7 miles northeast of Laguna Beach.