WASHINGTON – At least 30 letters containing suspicious powder have been mailed to Chase banks in nine cities but so far appear to be harmless, authorities said Tuesday.

The FBI said it was investigating 'a series of letters sent to banks around the country.'

'These threat letters contain a powder substance,' the FBI said in a statement. 'At this point, field tests on the powder have been negative. Additional testing will be completed. Even sending a hoax letter is a serious crime.'

A law enforcement official said the letters were mailed to Chase bank branches in or near Atlanta; Chicago; Columbus, Ohio; Dallas; Denver; Newark, N.J.; New York City; Oklahoma City; and Washington.

The letters all appear to be from the same source and were sent from Texas, the official said. They began showing up at the banks on Monday, according to the official who spoke on condition of anonymity because he was not authorized to discuss the matter publicly.

A city official in suburban Chicago, where two letters showed up at a Chase credit card processing center, said they were mailed from Amarillo, Texas. ....