PHOENIX, Nov 30 (Reuters) - An explosion and small fire on Friday outside a federal office building in southern Arizona caused minor damage and prompted an evacuation of the complex, but no injuries were reported, authorities said.
The blast occurred at about 8:30 a.m. near a rear doorway to the Social Security Administration building in downtown Casa Grande, a small city about 50 miles south of Phoenix.
Flames from the explosion were quickly extinguished Casa Grande Fire Marshal Barbara Rice said, adding that an unknown number of workers were ordered out of their offices as a precaution, and the building was cordoned off for investigation.
Local television news footage of the aftermath showed the frame of the metal security door blackened by the blast and fire.
"We don't have any information on what it was," Rice said. "We're waiting on a federal investigation to sort that out."
The FBI was leading a probe of the incident, since it occurred at a federal building, assisted by investigators from the U.S. Bureau of Alcohol, Tobacco, Fire and Explosives and local law enforcement.
An FBI spokesman could not immediately reached for comment. (Reporting by David Schwartz; Editing by Steve Gorman and Sandra Maler)