WILMINGTON, Delaware (Bloomberg) - Washington Mutual Inc., the bankrupt former parent of the biggest US bank to fail, sued JPMorgan Chase & Co., in an attempt to recover $4 billion in deposits.

Washington Mutual, known as WaMu, claims the money is being held by its former subsidiary, Washington Mutual Bank, which JPMorgan bought for $1.9 billion last year.

Seattle-based Washington Mutual has been trying to recover the money since filing for bankruptcy in September.

"JPMC has no basis to withhold the debtors' funds and the funds are accruing interest at a rate significantly less than what the debtors' estates would otherwise be earning," Washington Mutual said in court papers.

JPMorgan has declined to return the money, saying it may have a claim on the funds itself and that it cannot give Washington Mutual the money without receiving a so-called set- off right from the bankruptcy court, according to court papers filed by WaMu.

The set-off would ensure JPMorgan is paid for any claims it has against WaMu.

JPMorgan spokeswoman Christine Holevas declined to comment on the lawsuit.

The cash has inspired a battle in WaMu's bankruptcy case among its creditors and creditors of its former bank.

The US Federal Deposit Insurance Corp. said in court papers it may have a claim on the cash, while bondholders for Washington Mutual Bank claimed that the withdrawal would be unfair without forcing WaMu to prove it owns the cash.