A Chinese envoy met with North Korean leader Kim Jong-il Thursday to deliver a personal message and gift from President Hu Jintao as Washington appealed for cooperation by Asian powers on U.N. sanctions for Pyongyang's nuclear test.

"We want to leave open the path of negotiation. We don't want the crisis to escalate," U.S. Secretary of State Condoleezza Rice said in Seoul where she met with South Korean Foreign Minister Ban Ki-moon.

But Rice added: "Everyone should take stock of the leverage we have to get North Korea to return to the six-party talks."

The trip by State Councilor Tang Jiaxuan was the highest-level Chinese visit to its isolated ally since its Oct. 9 atomic test, and it came amid reports of a possible second nuclear test by Pyongyang.

Chinese Foreign Ministry spokesman Liu Jianchao said he had no details of the message conveyed by Tang, but said Kim and the diplomat had "in-depth discussions" about the nuclear dispute. North Korea's official Korean Central News Agency said Tang also brought a gift for Kim but did not say what it was.

"This is a very significant visit against the backdrop of major changes on the Korean Peninsula," Liu said at a regular news briefing. "We hope China's diplomatic efforts ... will bear fruit."

Hopes were also high that China could discourage the North from carrying out an apparent threat to stage a second atomic blast. Beijing has long been Pyongyang's closest ally and biggest trading partner.

A senior US official traveling with Rice reportedly said the Chinese envoy had gone to North Korea to tell the reclusive communist state not to conduct another test.

And Rice said openly at a press conference that she hoped the Chinese mission was successful in getting Pyongyang to scuttle its nuclear program.

U.S. media have reported that satellite images showed suspicious activity at a suspected North Korean nuclear site.

North Korea contends it needs nuclear weapons to counter U.S. aggression. The United States has repeatedly said it does not intend to attack the North or topple its communist government. The two Koreas remain technically at war, since the 1950-53 Korean War ended in a cease-fire that persists to this day.

After meeting with Rice, South Korean Foreign Minister Ban Ki-moon warned North Korea against doing anything more to stoke tensions. "A second nuclear test by North Korea should never take place," said Ban, selected this month to be the next U.N. secretary-general.

The North's nuclear test last week presented a serious challenge to U.S.-South Korean ties, which have long been strained by fundamental differences about how to deal with Pyongyang. The U.S. has called for a tougher line, while South Korea has been reluctant to take moves that could inflame tensions.

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South Korea, along with China, has been reluctant to comply with a sanction that calls for the inspection of cargo on ships sailing to and from North Korea. The Chinese have warned that the searches could unnecessarily provoke the North.

Rice told reporters in Seoul that there are many ways to implement the sanctions and it was up to each country to decide how it would comply and cooperate.

"I did not come to South Korea nor do I go anyplace else to try to dictate to governments what they ought to do," she said.

She added that early reports saying the U.N. sanctions would require a blockade or embargo on North Korean goods were exaggerated.

The South Koreans gave few signs that they would soon adopt Washington's hard-line approach with Pyongyang. The two sides urged North Korea to unconditionally return to the six-paty talks, which have been on hold since last year. The discussions also include China, Japan and Russia.

The South has faced criticism for a pair of landmark inter-Korean projects — a tourism venture and joint economic zone, both in North Korea — that are symbols of hopes for the peninsula's reunification.

Ban said Seoul would reconsider those projects "in harmony and in line with the U.N. Security Council resolution and international demands." He also said he explained the merits of the industrial zone to facilitate reforms in the communist nation, and that he believed the U.S. understood.

Earlier this week in Seoul, U.S. Assistant Secretary of State Christopher Hill criticized the tourism project, saying it appeared to simply funnel money to the North Korean regime.

Rice was reassuring Seoul that the U.S. stands behind its pledge to defend the country if the North attacked. She relayed a similar message in Japan, her first stop on a four-day trip devoted almost entirely to crisis talks on the nuclear threat. She leaves for China on Friday.

On Friday, Rice was to meet in Beijing with with President Hu, Premier Wen Jiabao and Foreign Minister Li Zhaoxing.

CountryWatch: North Korea

The Associated Press contributed to this report.