WASHINGTON (CNN) -- In a rare move, U.S. President George W. Bush has reached out, by letter, to North Korean leader Kim Jong Il, whom Bush has labeled a tyrant and part of what he called "the axis of evil."
North Korean leader Kim Jong Il appears at a summit luncheon in Pyongyang in October.
The letter urged North Korea to follow through on an agreement to declare and dismantle its nuclear programs, calling the moment a "critical juncture," U.S. Deputy State Department spokesman Tom Casey said Thursday.
"I want to emphasize that the declaration must be complete and accurate if we are to continue our progress," the letter said, according to a senior State Department official.
The letter to "Mr. Chairman" -- written on White House letterhead and signed "sincerely" by Bush's hand on December 1 -- was delivered by U.S. Assistant Secretary of State Christopher Hill, when he visited North Korea this week.
The letter was not intended to be a negotiating document but to show the United States is serious about keeping the process moving, Casey said. Watch how the letter is being described »
Bush also wrote letters about expectations for North Korea to the remaining members of the six-party talks which include Russia, China, South Korea and Japan.
In addition, Bush spoke by phone Thursday with Chinese President Hu Jintao about North Korea and Iran nuclear issues, as well as China-U.S. relations, according to China's Xinhua news agency.
"We are at an important point in six-party talks. We've moved from the suspension to disablement stage," Casey said.
Hill, the chief U.S. negotiator in the nuclear talks, described the disablement as "going well."
The big hurdle is an end-of-year deadline for North Korea to hand over a document declaring its nuclear secrets, past and present. Differences exist over what should go into that document and it's unclear how "full and complete" the list will be, Hill said.
Asked what the consequences would be if North Korea does not follow through, Casey responded, "The principle here is good faith for good faith. There are no guarantees."
He acknowledged there are sometimes obstacles and problems but added, "We believe we will get there."
Bush's letter is a positive sign, said analyst Joe Cirincione of the Center for American Progress, a liberal advocacy organization.
"It's a sign that the process is continuing and that it's taking place now at a more personal level. My interpretation is that Kim Jong Il would like a personal reassurance that the policy is actually endorsed by the president and that this will lead to the process of full diplomatic recognition between North Korea and the United States."
The news about the letter came as Bush tried to downplay the impact of a newly released assessment of another "member" of what he has called "the axis of evil." The National Intelligence Estimate concluded that Iran stopped work on a nuclear weapon in 2003. Bush, however, warns Iran could restart the program and is still considered "dangerous." E-mail to a friend