CASA GRANDE, Ariz. -- The FBI is investigating an explosion at a federal building in downtown Casa Grande on Friday.
Sources tell 3TV that authorities are questioning a person of interest in the case.
Police and fire crews responded to the explosion at the Social Security Administration building, 501 N. Marshall St., at approximately 8:15 a.m. The building is across the street from the Casa Grande Police Department.
Upon arrival, police and fire officials learned that the explosion came from a device that detonated at the back door of the building, according to city spokesman Agustin Avalos. The device is unknown at this time.
Fire Marshal Barbara Rice said a fire was quickly extinguished, but there was some damage to the exterior of the building.
A number of staff members were in the office at the time of the explosion, but no injuries were reported.
The building was evacuated and the scene was cordoned off. Rice said nearby buildings were not evacuated.
Rice said the incident appears to be a deliberate act, but that has not been confirmed.
FBI officials are unable to confirm or deny whether anyone is in custody.
Casa Grande is about an hour south of Phoenix via Interstate 10.
Details will be updated as they become available.