WASHINGTON (Reuters) - Seven Chase bank branches in Phoenix and the New York Times headquarters in New York received envelopes containing a suspicious white powder on Wednesday as a wave of threatening U.S. mailings spread.

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More than 45 threatening letters have been received since Monday at financial institutions in at least 11 states, FBI spokesman Richard Kolko said. “Most of the letters contain a powder substance with a threatening communication,” he said.

No harmful substances have yet been identified but more tests are being conducted at regional laboratories, he said.

U.S. authorities are always on the alert for such letters after incidents in 2001 in which envelopes laced with anthrax were sent to media outlets and U.S. lawmakers, killing five people and further rattling a nation shaken by the September 11 attacks.

Asked if the bank letters were sent by a single mailer, Kolko said, “there’s certainly a common thread.”

A Dallas-area office of the Federal Deposit Insurance Corporation also received a suspicious letter, he said.

He said it was not clear whether the New York Times incident was related. Times spokeswoman Catherine Mathis said police were called this morning after an employee on the 13th floor opened an envelope addressed to the paper.

“A white granular substance was in the envelope. The New York City police were called and are now on site investigating,” she said in a statement, adding that part of the lobby was closed and no one had been sent to hospital.

“People are able to get in and out of the building. The substance will be tested,” she said.

In Phoenix, no workers at the banks were treated for any symptoms, said Capt. Shelly Jamison, a Phoenix Fire Department spokeswoman. Authorities said seven branches received letters, and bank officials said not all the letters were opened, after employees were alerted to their appearance.

FBI spokesman Manuel Johnson in Phoenix said it was too early to establish a link between the letters received there and the others.

The FBI, U.S. Postal Inspectors and local authorities are investigating the letters. The letters have been received at branches in Arizona, California, Colorado, Georgia, Illinois, New Jersey, New York, Ohio, Oklahoma, Texas and Washington, D.C., the FBI said.

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