"As many have heard me say before, the whole issue related to BDA was a lot more complicated than anybody could have possibly anticipated," State Department spokesman Sean McCormack said at a briefing.

"The rules, regulations and traditional behaviors in the international financial system make this sort of resolution very complicated," McCormack said.

However, the United States wants the matter to be resolved as soon as possible in order to get back to implementing the February 13 agreement, McCormack said.

The United States has said it is willing to give the DPRK more time to resolve the complex BDA issue.

Because of the lingering financial disputes between the United States and the DPRK, the DPRK missed an April 14 deadline to shut down its main nuclear reactor, which was specified as the first implementation phase of the February 13 disarmament agreement.

The DPRK has pledged to fulfill its commitment to implement the February 13 agreement, saying it would invite the International Atomic Energy Agency (IAEA) delegation to the country once it retrieves the 25 million dollars in funds frozen in the BDA.