US president George Bush has called on North Korea to provide a full declaration of its nuclear activities.
Speaking at a news conference with new South Korean President Lee Myung-bak at the US presidential retreat in Camp David, Maryland, said North Korea may be trying to stall.
"Now North Korea must fulfill its other obligations to provide a full declaration of its nuclear programs and proliferation activities in a verifiable way," Mr Bush said at a news conference with South Korean President Lee Myung-bak.
North Korea, which tested a nuclear device in 2006, failed to meet a December 31, 2007, deadline to reveal the extent of its nuclear weapons programs in a deal with the United States, China, South Korea, Japan and Russia.
If Pyongyang makes the declaration, the United States is expected to ease sanctions. A team of experts plans to go to the reclusive country next week to see if inroads can be made on finishing the report about its nuclear program.
"They may be trying to stall," Mr Bush said. "One thing about a non-transparent society where there is not a lot of free press, for example, or a lot of opposition voices, it's hard to tell what's going on."
But Mr Bush said the countries in the six-party talks with North Korea were waiting to see whether Pyongyang complies, and that he was "hopeful."
President Bush also said US Congress must approve a free trade agreement with South Korea this year, calling it a "priority" for his administration.