JPMorgan Chase chief executive Jamie Dimon and dozens of JP Morgan executives in 11 US cities, along with banking regulators, have received at least 50 anonymous death threat letters, with a dire warning of a series of attacks ending in an Oklahoma City-like bombing because Morgan's acquisition of Washington Mutual in a deal brokered by the US government, for a fraction of the price that had been offered for the group in March.

WaMu was initially acquired by the US government and later sold to JPMorgan for $1.9 billion, and under the deal brokered by the US government, all WaMu depositors' money was guaranteed, but holders of debt and preferred stock were practically wiped out.

Jamie Dimon, seen by many seen as a potential US treasury secretary if Barack Obama wins the presidential election, was the target for the threats, with one letter saying "You need to be pay back. You will be killed in 10 days."

Another, letter to the bank chief warned of a terror attack, similar to the Oklahoma City-like bombing.

All letters, typewritten and from the same source, contained harmless calcium powder with a series of spelling mistakes ''Steal tens of thousands of people's money and not expect reprercussions,'' read one, which was written in all capital letters and includes the misspelling. The letter also said, ''It's payback time. What you just breathed in will kill you within 10 days.''

Threat letters containing similar powder was received by The New York Times, the Los Angeles Times and the campaign offices of Senator Barack Obama in New York, Philadelphia and Los Angeles.

At least 45 letters bore the postmark of Amarillo in Texas and was mailed on 17 October and 18 October, to the Federal Deposit Insurance Corporation, the office of Thrift Supervision in Dallas and the Federal Home Loan Bank in Atlanta.

The letters were also mailed to Chase bank branches in Atlanta, Chicago, Columbus, Ohio, Dallas, Denver, Newark, N.J., New York City, Oklahoma City, Phoenix, San Francisco and Arlington, Virginia.

The US Postal Inspection Service has got into the act by offering a $100,000 reward for information relating to the letters.

The FBI, which is investigating the case, said, "We are following several good leads, but we are always looking for more information."