North Korean leader Kim Jong Un arrived in China on Tuesday for a four-day trip during which he and Chinese President Xi Jinping are expected to coordinate strategies ahead of a possible second summit with the United States amid stalled denuclearization talks.

Kim, who is believed to have celebrated his 35th birthday on Tuesday, was seen getting off his special armored train with wife Ri Sol Ju in Beijing just before 11 a.m. Tuesday after leaving North Korea the day before. Several North Korean officials, including Kim's sister, Kim Yo Jong, and the despot’s right-hand man, Kim Yong Chol, were also spotted in the Chinese capital, South Korea's Yonhap News Agency reported.

The North’s Korean Central News Agency said Xi extended an invitation to Kim. This marks Kim’s fourth visit to China in less than a year.

Details of the visit were not released, but Kim’s visit follows his New Year’s Day address in which he pledged to build peace in the Korean Peninsula while building his country’s economy despite the crippling international sanctions. China is North Korea’s most important trading partner and a key buffer against pressure from the U.S.

Chinese foreign ministry spokesman Lu Kang gave no details about Kim's schedule or China's role as an intermediary between the U.S. and North Korea. But he said Beijing remains supportive of efforts to end tensions over U.S. demands for a halt to North Korea's nuclear and missile programs.

"We always believe that, as key parties to the Korean Peninsula issue, it's important for the two sides to maintain contact and we always support their dialogue to achieve positive outcomes," Lu told reporters at a daily briefing.

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Yang Moo-jin, a professor at the University of North Korean Studies, told South Korea’s Yonhap News agency that North Korean leaders rarely make foreign trips early in the year. The early announcement of Kim’s trip to China also showed possible growing confidence between the two countries.

"It is rare that the North's leader travels overseas at the start of the year. [His trip to China] shows how important it is to advance relations between the North and China," Yang said. "It is also aimed at showing off the image of a leader of a normal state.”

Last year marked unprecedented progress in denuclearization talks, with Kim holding summits with Trump, Xi and South Korean President Moon Jae-in. But despite a cooling of relations last year with China over the imposition of sanctions, China has and remains the Hermit Kingdom's most important economic and diplomatic ally.

KIM JONG UN MAKES 4TH TRIP TO CHINA, CHINESE STATE MEDIA REPORTS

Harry J. Kazianis, director of defense studies at the U.S.-based Center for the National Interest, said Kim’s overtures to China suggest he “is eager to remind the Trump administration that he does have diplomatic and economic options besides what Washington and Seoul can offer,” adding that his New Year’s Day speech may suggest a “veiled threat to move closer to Beijing.”

The Kim-Xi meeting coincides with talks this week between a U.S. delegation and Beijing to de-escalate the ongoing trade war between China and the U.S.

U.S. Secretary of State Mike Pompeo told CNBC on Monday that he did not think the trade dispute with Beijing would affect China’s efforts at resolving the North Korean crisis.

Xi is also expected to visit North Korea this year to mark the 70th anniversary of the neighboring countries establishing diplomatic ties. Lu told reporters on Tuesday that information about the Chinese president’s visit would be “released in due course.”

The Associated Press contributed to this report.

The Associated Press contributed to this report.