Top executives at JPMorgan Chase & Co got blunt warnings about speculation that Bernard Madoff was running a Ponzi scheme, but appear to have been concerned only with protecting the bank's own investments, the trustee seeking to recoup $6.4 billion for Madoff investors said.

Irving Picard, the trustee, announced the allegation in connection with his unsealing of his complaint against the bank, which was originally filed in December with the federal bankruptcy court in Manhattan.

The case is Picard v. JPMorgan Chase & Co et al, U.S. Bankruptcy Court, Southern District of New York, No. 10-ap-04932.

(Reporting by Jonathan Stempel in New York; Editing by Phil Berlowitz)