"BDA has been a tough issue for people to work on. It's been a tough technical issue. But people are continuing to work through it and we are hopeful that it will be resolved as soon as possible, " State Department deputy spokesman Tom Casey said at a briefing.

"We'd like to see the North Koreans move as quickly as possible to meeting their commitments under the February 13 agreement. I think we're all agreed that a lot of time has gone by. We definitely want to get back on track to the main focus of these talks, which is denuclearization of the Korean Peninsula," Casey 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 delegation to the country once it retrieves the 25 million dollars in funds frozen in the BDA.