DENVER (Reuters) - At least five branches of Chase bank in Colorado and Oklahoma received threatening letters on Monday, some containing an unidentified white powder.

A woman walks past a JP Morgan Chase bank branch in New York, October 15, 2008. REUTERS/Lucas Jackson

A spokeswoman for Chase said the letters were delivered to three branches in the Denver area and locations in Oklahoma City and Norman, Oklahoma.

Some of the envelopes contained the white powder, Chase spokeswoman Mary Jane Rogers said, and one employee was treated for a rash as a precaution, but it was not clear if the skin irritation was caused by the powder or had already been there.

She identified the Colorado branches as being in Lakewood and Arvada.

Fire Marshal Kevin Ferry of the Cunningham Fire Protection District near Denver said the powder in one package was found to be harmless, though the substance had yet to be identified.

That branch was inside a supermarket in the Denver suburb of Centennial. The supermarket was evacuated as a precaution.

Several bank employees who had close contact with the package were sent to a local hospital for evaluation, he said.

A police department spokesman in nearby Lakewood, Steve Davis, said a white substance found on a parcel there appeared not to be dangerous and resembled talcum powder.

JPMorgan Chase & Co last week surpassed Citigroup Inc to became the largest U.S. bank, and has aggressively acquired other assets as the financial system has weakened, including the banking assets of Washington Mutual Inc.

Rogers said Chase would not release the total number of banks affected until they were sure all the letters had been found.

“We immediately called the FBI and Postal Inspection Service to handle the matter and ensure the safety of our customers and employees,” Rogers said.

She did not know the contents of the letters or if they contained return addresses.