Washington Mutual Inc has asked a bankruptcy court to rule on its dispute with JPMorgan Chase & Co over more than $4 billion in deposits, according to court documents on Wednesday.

Washington Mutual Bank was closed by the U.S. government in September, in one of the largest bank failures in U.S. history. Its banking assets were sold the same day to JPMorgan for $1.9 billion, and the parent holding company filed for bankruptcy protection a day later. The company is seeking the return of the cash deposits, to which it lost access when the bank was sold.

JPMorgan is withholding deposits without any legitimate factual or legal basis, according to court documents.

WaMu has said it needs access to that cash to come up with its Chapter 11 plan, and that by withholding the deposits, JPMorgan could be earning as much as $200 million per year in interest on those deposits.

A JPMorgan Chase spokesman in New York said the company had no comment.

The lawsuit was filed as an adversary proceeding to WaMu's main bankruptcy case.

The bankruptcy case is In re: Washington Mutual, Inc. U.S. Bankruptcy Court, District of Delaware, No. 08-12229. (Reporting by Emily Chasan, writing by Chelsea Emery, editing by Dave Zimmerman)