U.S. Secretary of State Condoleezza Rice is urging North Korea to accept the proposed terms of the verification process on its nuclear activities.
Rice told reporters in Singapore Thursday that the declaration North Korea made last month on its plutonium production leaves many unanswered questions.
She said no one will trust what North Korea says about its nuclear activities unless the declaration is verified using internationally-recognized methods.
A North Korean spokesman, Ri Tong-il, said all issues, including verification, would be resolved if Washington follows through with its promises.
The United States has agreed to remove North Korea from a list of state sponsors of terrorism, if Pyongyang abandons its nuclear program. The deal also will provide Pyongyang with food and fuel aid.
On Wednesday, Rice held her first-ever meeting with her North Korean counterpart, Pak Ui-chun, on the sidelines of a regional Asian forum in Singapore.
Wednesday's meeting also included the foreign ministers from Japan, China, South Korea and Russia - the four other nations involved in North Korea's disarmament process.
Officials attending the Association of South East Asian Nations forum said the organization wants to help North Korea end its isolation.
The grouping's chairman, Singapore Foreign Minister George Yeo, urged North Korea to follow the same path of economic liberalization as communist Vietnam.
Earlier this month, Pyongyang agreed to disable its main plutonium-producing facilities by the end of October, and allow on-site inspections to verify the process.
The chief U.S. nuclear negotiator, Christopher Hill, says he hopes there can be an agreement on the verification process by mid-August.
Efforts to disarm North Korea's nuclear program intensified two years ago, when Pyongyang conducted its first known test of a nuclear weapon.