SEOUL (Reuters) - China said on Thursday it had sent diplomats on a visit of major significance to North Korea amid speculation that its communist neighbor might be about to detonate a second nuclear device. Beijing's rare direct appeal to reclusive North Korea came as U.S. Secretary of State Condoleezza Rice played down differences with South Korea and China over U.N. sanctions imposed on Pyongyang, saying Washington had no wish to escalate the crisis. "We want to leave open the path of negotiations," Rice told a news conference with South Korean Foreign Minister Ban Ki-moon in Seoul, the second leg of a tour that began in Tokyo and will take her to Beijing on Friday. China, North Korea's strongest backer, announced earlier that it had sent a high-level delegation to Pyongyang. "This visit was very important," Chinese Foreign Ministry spokesman Liu Jianchao said. "It has major significance." The Chinese officials, who included state councilor and former foreign minister Tang Jiaxuan, delivered a message to Kim Jong-il from President Hu Jintao. Tang arrived in Pyongyang on Wednesday with Chinese Vice Foreign Ministers Dai Bingguo and Wu Dawei, who is also China's chief negotiator to long-stalled six-party talks to end North Korea's nuclear weapons program. "I hope it (China) has been successful in saying to North Korea that there is really only one path, which is denuclearization and dismantlement of its programs," Rice said. "What I do think is very important is everyone take stock of the leverage we have to get North Korea to return to the six-party talks and negotiate seriously the dismantlement of its nuclear weapons programs." North Korea's state news agency, KCNA, in an unusually quick report for a meeting with Kim, said the talks with the Chinese envoy had been conducted in a "friendly atmosphere." "Discussed there were the issues of developing the relations of friendship between the two countries and ensuring peace and security on the Korean Peninsula and a series of international issues of mutual concern," it said. SECOND TEST? A senior U.S. official with Rice said he believed Tang had gone to tell the isolated state not to conduct another test. North Korea's first-ever test, on October 9, drew worldwide condemnation and a U.N. resolution authorizing financial and weapons sanctions on the country. But a senior State Department official said he did not expect any "surprise announcement" when Rice met Tang in Beijing. "Our understanding is that the North Koreans have not been in the mood to return to (six-party) talks. If anything they are looking to escalate the crisis further," said the official, who asked not to be identified. As Rice began her trip to the region on Wednesday, U.S. intelligence experts said satellites had spotted an increase in activity at a suspected nuclear test site in North Korea. U.S. and South Korean officials said there was no sign another test was imminent. But a South Korean lawmaker and parliamentary intelligence committee member, Chung Hyung-keun, said the North could be preparing three or four more tests. Washington is worried that Japan and South Korea might build up their own weaponry in response to North Korea's nuclear test. In South Korea, as in Japan, Rice reaffirmed Washington's commitment to defend its Asian allies. In a demonstration of unity, Rice, Ban and their Japanese counterpart, Taro Aso, held talks in Seoul -- the first such meeting of the three countries' foreign ministers for six years. "It was very meaningful. We were able to show clearly today that Japan, the U.S. and South Korea stand on common ground," Aso told reporters later. Rice played down differences with Seoul and Beijing over the implementation of sanctions and stressed that Washington had no intention of imposing a blockade on the impoverished country. "The idea that we would do something ... that escalates tensions on the Korean peninsula or on the high seas for that matter could not be more wrong," she said. China fears a heavy-handed approach to inspections of cargo at sea may provoke military confrontations and stoke tensions on the Korean peninsula. It is also wary about squeezing its food and energy lifeline to Pyongyang, fearing this could lead to an exodus of refugees and even the ultimate implosion of the state. China's Liu warned at a news conference against "willfully" expanding U.N. sanctions. "Sanctions are a signal, not the goal," he said.