In return for telling the truth, the letter said, the US could be ready to establish full diplomatic ties and other relations.
"The declaration must be complete and accurate if we are to continue our progress"
"I want to emphasise that the declaration must be complete and accurate if we are to continue our progress," Bush reportedly wrote.
The letter comes amid mounting concerns in the US and other countries party to the agreement that the December 31 deadline will be missed.
It was delivered to North Korea's foreign minister during a visit to the country this week by Christopher Hill, the top US nuclear negotiator.
Dana Perino, a White House spokeswoman, said Bush had warned in the letter, dated December 1, that the disarmament deal stood at a "critical juncture".
A full transcript of the letter has not been released, although Perino said it began "Dear Mister Chairman" and was personally signed by the president.
US officials have sought to play down the significance of the letter, but observers say it reflects a changing approach to North Korea.
'Last ditch attempt'
|Bush has previously labelled Kim a "tryant" and, |
according to one report, a "pygmy" [Reuters]
Bush has previously made little secret of his dislike for the North Korean leader, once publicly referring to Kim as a "tyrant" and, reportedly, a "pygmy".
Korea analyst Donald Kirk, who is based in the South Korean capital Seoul, told Al Jazeera the letter would be symbolically important to the North and would be seen as a sign that the US was eager to see the deal completed.
The letter was a "last ditch attempt to get North Korea to come clean" about its nuclear weapons programmes, Kirk said.
Perino said the message to the North was a firmly worded "reminder" to the North Korean leader over it obligations, saying: "It is up to you, North Korea, to make a complete and accurate declaration."
Without that, she said, the US would know North Korea was not honouring the aims of the agreement.
The North has so far made no comment on the letter, other than a brief two sentence report from its official news agency on Thursday confirming it had been received.
"Being clear about what's happened is also a means for us to build a future relationship"
chief US nuclear envoy
Bush also reportedly sent letters to the leaders of China, Russia, Japan and South Korea, the other parties involved in the process to dismantle North Korea's nuclear programme.
A fresh round of six-nation talks had been expected to take place in Beijing this week, but on Tuesday the US state department announced that the meeting had been put off due to "logistical and scheduling" issues.
China, the host of the talks, has not said whether talks will take place before the end of the year, saying only that diplomats were working on suitable dates.
Speaking in Beijing on Thursday, Hill, the US nuclear envoy, said the Bush administration "felt we were at a crucial moment and it was important to reach out to all the parties, and that's what the president did."
Hill travelled to North Korea earlier this week and toured the Yongbyon nuclear reactor complex to assess progress on disabling the plant under the terms of the February agreement.
He said North Korea's co-operation on that issue had been "excellent" and was "really moving ahead".
"Anyone who has seen it can see that it is on schedule," he said.
|US and international experts are overseeing |
work to disable the Yongbyon plant [EPA]
But while work continues at the plutonium-producing Yongbyon plant, concerns have been growing over North Korea's commitment to declaring its other nuclear activities and facilities, particularly an alleged programme to develop weapons-grade uranium.
Producing enriched uranium for use in nuclear weapons does not require a nuclear reactor, and the US wants to see a full accounting of North Korea's activities in this area.
A particular concern has been allegations that it brought sophisticated gas centrifuges, used in the enrichment process, from Pakistan.
On Thursday Hill said he had had "a lot of discussions" with North Korean officials during his visit about uranium enrichment, adding that the US had "very good evidence" that the North had received technology and assistance from Pakistan.
Hill said that it was essential to future progress for the North to tell all about its nuclear weapons efforts, even programmes which had proved fruitless or been abandoned.
"We want to be completely sure they don't have any ongoing programme," he said.
"Being clear about what's happened is also a means for us to build a future relationship."
Washington also wants to see North Korea address concerns over weapons proliferation, raised most recently by allegations over possible nuclear ties between North Korea and Syria.
In addition, questions remain over how many nuclear weapons North Korea has already produced, if any, and what will happen to them.
North Korea conducted its first test of a plutonium-based nuclear weapon in October last year, although it is unclear how much of a success it was.
Critics in the US have condemned the deal with North Korea as overly generous and relying too much on an unreliable country.
Many have argued that Bush has given too many concessions to Pyongyang, in an effort to score a foreign policy success before he leaves office and distract attention from failing US policies in Iraq.