nuclear crisis negotiations.....

BEIJING, China (CNN) -- Despite the lack of any significant breakthrough, the United States says six-party talks on the North Korean nuclear crisis exceeded expectations and declared them "very successful."

The four-day meeting concluded Saturday with a tentative agreement to meet again in Beijing and a warning from China that "a long and bumpy road still lies ahead."

No date was immediately announced but there was an additional pledge to create lower-level working groups to help find a resolution to the crisis.

However, intensive last minute negotiations were unable to craft a joint statement to round off the talks.

Analysts say the lackluster conclusion provides little evidence that the diplomatic gulf between North Korea and the United States has narrowed at all, despite various reports during the talks of positive progress towards ending the crisis.

China -- which hosted negotiators from North and South Korea, Japan, Russia and the U.S. -- was hard pressed to put a positive spin on the outcome of the talks.

"Some people are disappointed with the outcome of meetings, which was not as substantial as they have expected," Chinese Foreign Minister Li Zhaoxing said. "However, we should highly value efforts made by all sides in this process."

But the U.S. was buoyed after all but the North agreed to the goal of complete, verifiable and irreversible dismantlement of Pyongyang's nuclear programs.

A senior U.S. official told reporters in Beijing on Saturday that Pyongyang's denial of its uranium-based weapons program at the talks was only resulting in its "self-isolation."

"The event has exceeded my expectations in a very important respect. It's been very successful in moving the agenda towards our goal of complete, verifiable and irreversible dismantling (CVID) of DPRK nuclear programs," the U.S. official said on condition of anonymity.

"CVID is now more on the table than ever."

The United States and North Korea met twice for one-on-one discussions, the official added.

China's negotiator at the talks Wang Yi said no consensus had been reached on the definition and scope of the U.S. proposal for the scrapping of Pyongyang's nuclear program.

Yi added that North Korea's proposal of a "freeze" of its program needed to be further discussed.

He said an "extreme lack of trust" was the main reason for the impasse at the talks.

N. Korean offer

Waxing flowery language about passages of the seasons with warm farewells, China's Li said "serious differences" still exist between parties.

"Even the most difficult tasks can be accomplished if we work hard enough. I think spring is a season of promises ... Let's be committed to the process of talks for peace, be committed to the direction of peacefully resolving the issue, and make our efforts to writing a new chapter featuring reconciliation and cooperation," he said.

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^^^^North Korea offered to get rid of its nuclear weapons if the United States assures its security.^^^^

The closing of the talks on Saturday was delayed for several hours due to "technical reasons," Chinese officials said, amid reports North Korea was demanding last minute revisions to a planned joint statement.

It was unclear what North Korea wanted to alter in the joint statement.

The three-day talks were highlighted by an offer by North Korea to end its nuclear weapons program. While no details on the offer were made public, it is unlikely the proposal met the United States' criteria of a complete, verifiable, and irreversible dismantling of Pyongyang's nuclear program.

After announcing Thursday its long stated demand that North Korea would get rid of its nuclear weapons if the United States assured its security, Pyongyang blamed a "hardline" U.S. stance for impeding the talks and insisted Washington end what it called "hostile actions."

Pyongyang wants a non-aggression treaty with the United States, or at least a security guarantee from all five of its negotiating partners, before it halts its nuclear program.

Washington has refused to sign a non-aggression treaty with North Korea or offer aid to the country, saying it will not give into blackmail. But the U.S. has said it was prepared to offer North Korea a written security guarantee.

The standoff between the United States and North Korea flared in October 2002 when U.S. officials said Pyongyang admitted to secretly pursuing a nuclear weapons program.