North Korean leader Kim Jong-un on Tuesday left Pyongyang by train for a surprise visit to Beijing.

Accompanied by his wife Ri Sol-ju and other top officials, the Korean leader boarded a morning train departing for China for a four-day visit.

According to North's Korean Central News Agency, Kim's trip to China came after an invitation by Chinese President Xi Jinping.

The two leaders are speculated to coordinate ahead of Kim's next round of negotiations with US President Donald Trump projected to be held early 2019.

While the Singapore Summit between Kim and Trump came as a breakthrough in the nuclear crisis of Korean Peninsula, progress has stalled since then.

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