Washington promised to resolve the issue by mid-March as part of an agreement last month on North Korea's nuclear disarmament.
On Saturday, North Korea's nuclear envoy said Pyongyang would not shut down its main nuclear reactor until the funds were released.
Meanwhile, the US envoy to talks on the North's nuclear programme has said that North Korea was on track to fulfil its side of a breakthrough disarmament accord by shutting down its main atomic facility next month.
Christopher Hill, the US chief negotiator, said on Sunday: "I think we are on schedule for the shutdown of the facilities and monitoring by the IAEA".
North Korea agreed at six-party talks in February that group the two Koreas, the US, host China, Japan and Russia to shut its Yongbyon reactor and readmit inspectors from the International Atomic Energy Agency within 60 days.