The trustee seeking money for defrauded former clients of Bernard Madoff said he filed a $6.4 billion lawsuit accusing JPMorgan Chase & Co. of aiding the imprisoned Ponzi schemer's fraud as his main banker.

"JPMorgan was willfully blind to the fraud, even after learning about numerous red flags surrounding Madoff," said David Sheehan, a partner at Baker & Hostetler LLP and counsel to Irving Picard, the court-appointed trustee.

The second-largest U.S. bank was for more than 20 years the primary banker for Bernard L. Madoff Investment Securities LLC, the trustee said.

Picard said his lawsuit seeks to recover nearly $1 billion in fees and profits, plus $5.4 billion in damages.

In an e-mailed statement, JPMorgan called any suggestion that it supported Madoff's fraud "utterly baseless and demonstrably false," and said it will defend against the lawsuit.

The trustee filed his complaint under seal with the U.S. bankruptcy court in Manhattan. A copy of the complaint was not immediately available. A spokesman for Picard did not immediately respond to a request for a copy.