China's president issued an unusual public appeal Tuesday to a visiting North Korean official to avoid aggravating tensions with its missile test program, as the U.S. and Japan urged Beijing to press its ally Pyongyang for concessions.

U.S. nuclear envoy Christopher Hill arrived in Beijing for his second visit in a week amid urgent diplomatic exchanges, saying talks were in a "crucial period." He said he had no plans to meet with the North Korean official.

A Chinese Foreign Ministry spokeswoman criticized a Japanese proposal that demands that the North stop developing, testing, deploying and selling ballistic missiles as "an overreaction."

Cabinet-level talks between North and South Korea, meanwhile, kicked off with the South telling its northern neighbor that Pyongyang's missile tests were destabilizing the region.

President Hu Jintao told the visiting vice president of the North's parliament, Yang Hyong Sop: "We are against any actions that will aggravate the situation. We hope that relevant parties will do more things conducive to the peace and stability of the peninsula," according to the official Xinhua News Agency.

Hu said Beijing is "seriously concerned" and called for progress in stalled six-nation talks over the North's nuclear program.

CountryWatch: North Korea

The warning by Hu, who rarely speaks publicly about North Korea, represented an unusually firm stance by Beijing and appeared to reflect growing frustration with its unruly ally.

Hill said Washington was counting on Beijing to take the lead in lobbying the North to stop missile tests and return to nuclear talks.

"China clearly has a close relationship with the DPRK and the most influence, and we certainly would like to see what kind of leverage China has," Hill said, referring to the North by the initials of its formal name.

Hill arrived from Tokyo following talks with Japanese officials as part of an Asian tour to coordinate a response to North Korea's missile tests last week, including a long-range Taepodong-2 potentially capable of hitting the United States. The weapons, which landed in the waters between the Korean Peninsula and Japan, created a major new challenge for the six countries trying to defuse the North's nuclear threat.

So far, the nations have struggled to find a consensus on how to handle the crisis. The discord and division has likely delighted the reclusive communist nation, which often tries to drive a wedge between the nations seeking to pacify Pyongyang.

Hill said he added a second stop in Beijing to gauge the progress made by Chinese diplomats with the North. He said he had no plans to meet with the North Koreans, whose government has refused to return to nuclear talks until Washington lifts sanctions meant to punish the North for money-laundering and other offenses.

"Our position has been pretty firm on this," he said. "We meet with all the delegations, including the DPRK ... but they have to be in the six-party process."

Hill said "the jury is still out" on whether Pyongyang was ready to carry out a joint statement issued in September at six-nation talks that calls for the North to renounce nuclear development in exchange for aid and a security guarantee.

China, South Korea, Japan and Russia are the other participants in the negotiations.

U.N. Security Council members on Monday agreed to delay a vote on a Japanese proposal to sanction the North over the missile tests in hopes that China, the isolated regime's main ally and aid donor, can persuade it to refrain from any more launches.

Chinese Foreign Ministry spokeswoman Jiang Yu said adoption of the proposal "will cause an escalation of tensions and further intensify the problem ... and undermine efforts to resume the six-party talks."

Instead, Beijing proposed a nonbinding U.N. statement that called for renewed talks on the North's nuclear programs.

"China is gravely concerned about the current situation and we have expressed our position to the DPRK side over the past days," Jiang said without elaborating.

The North Korean envoy, Yang, was beginning a five-day visit to Beijing to mark the 45th anniversary of a friendship treaty between China and North Korea. A Chinese delegation including Beijing's chief nuclear negotiator, Wu Dawei, was in Pyongyang on a reciprocal visit.

At a dinner marking the start of a four-day gathering in Busan, South Korea, envoy Lee Jong-seok told the North's delegation Pyongyang's missile tests was "making the situation in the region unstable and is also affecting South-North relations."

North Korea's chief delegate Kwon Ho Ung said that he would try to make the talks a success and that the Koreans should stick together.

"No matter how the situation changes and the environment becomes different, both the North and the South, without going off this rail, should go to the end on the path" of reconciliation, Kwon said.