If it is true, Kim's trip could provide a crucial momentum to resolve the security crisis on the Korean peninsula fueled by the North's recent missile tests and reported moves toward a nuclear test, officials and analysts say.

According to news reports in Seoul. South Korean officials obtained intelligence that a special train used by Kim was seen crossing the North's northeast border with China on Tuesday.

"There is intelligence that the United States or Russia have confirmed through satellite photography that a special North Korean train was moving in China," a South Korean government source was quoted as saying. The source said, however, it was not clear whether Kim was aboard the train.

Seoul's YTN television also said the government has received intelligence reports that the special train headed for China. The North Korean leader has used a special train rather than aircraft for visits to China or Russia because of his alleged fear of flying.

Rumors of Kim's possible visit to China had been earlier reported from Seoul and Tokyo last week. South Korea's most influential Chosun Ilbo newspaper said that a senior military official from the North was staying in Beijng to discuss summit talks with Hu slated for this week. "Authorities in Seoul and Washington were briefed that Kim Jong Il is to take a three-day trip to China around Aug. 30," it said, citing sources.

The semi-official Yonhap News Agency reported that the Chinese government has invited Kim Jong Il to visit "as soon as possible." Japan's Sankei Shimbun newspaper also said Kim was expected to travel to China this week, citing multiple sources.

South Korean government officials declined to confirm the reports. "We can't officially confirm the reports. Kim's visit is only a possibility," said Choo Kyu-ho, spokesman for South Korea's Foreign Ministry.

Other officials said they were still checking the reports. "As of now, we do not have any evidence," a government official said.

Speaking on condition of anonymity, he said there have been no preparatory security measures that were detected in the past before Kim's travel on a special train. "If Kim's special train crosses the border, security guards used to be dispatched first to border towns," he said.

But officials said they could not rule out Kim's visit to China because his trips have been surrounded in tight secrecy. Kim has traveled to China several times, but Pyongyang and Beijing acknowledged the trip only after he returned home.

"We are keeping close watches on Kim's possible visit to China," the official said. "If realized, the visit would be focused on the North's nuclear activities and strained relations between Pyongyang and Beijing," he said.

Analysts say Kim may be frustrated by China's recent moves following the North's missile tests on July 5. China has signaled anger over North Korea's missile launches against its advice, which could prompt rival Japan to build up military forces, they said.

China, along with Russia, approved the U.N. resolution presented by Japan and the United States condemning North Korea for its missile launches and barred the country from acquiring or selling missile technology and materials related to weapons of mass destruction.

China has also frozen North Korea's suspicious bank accounts, joining the U.S. campaign to clamp down on the communist state's alleged financial crimes.

Beijing has reportedly reduced its food and oil supplies to the North in a punishment. China holds the key to the North's economic survival because it is the key supplier of food and fuel to the impoverished, isolated country.

China's crackdown on cross-border traffic could deliver a major blow to North Korea which has been increasingly dependent on China, analysts say.

"I see a possibility about Kim's visit as he may feel the need to break the strained ties with China," Paek Seung-joo, an analyst at the Korea Institute for Defense Analysis in Seoul.

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