Police officers escort bystanders away as they secure the area after at least one person opens fire at a social services agency in San Bernardino, California, Dec 2, 2015. [Photo/Agencies]

"We have no information at this point that this is terrorist-related, in the traditional sense that people may be thinking," he added. "Obviously, at minimum, we have a domestic-type terrorist-type situation that occurred here."

He said the suspects were armed with rifles.

The Inland Regional Center is one of 21 facilities set up by the state and run under contract by non-profit organizations to serve people with developmental disabilities, said Nancy Lungren, spokeswoman for the California Department of Developmental Services.