WASHINGTON (CNN) -- The FBI and the Postal Inspection Service are investigating more than 30 angry letters containing a white powdery substance recently sent to banks, officials said Tuesday.
Officials said most of the powder-laced letters were sent to branches of JPMorgan Chase.
The FBI said the letters have not posed a health threat.
"At this point, field tests on the powder have been negative. Additional tests will be completed," FBI spokesman Richard Kolko said in a written statement.
The letters contained a message of anger concerning the "banking situation," the law enforcement official said.
Investigators refused to speak on the record discussing the notes in more detail because the investigation is ongoing.
Bank branches in Colorado, Oklahoma, Illinois, New York, New Jersey, Ohio, Georgia, Texas and the District of Columbia received letters Monday, the official said.
The official said most of the letters have been sent to branches of JPMorgan Chase. Not all of the recipients were banks, officials said. Letters were also sent to the offices of the Federal Deposit Insurance Corporation and the Office of Thrift Supervision.