Seoul, South Korea - A train carrying North Korean leader Kim Jong Un passed into China early Tuesday, South Korea's Yonhap news agency reported, citing the North's state-run radio service.

It is a rare trip outside North Korea for Kim, who is one of 26 heads of state slated to attend a military parade in Beijing to mark the 80th anniversary of Japan's surrender in World War II.

If it proceeds as planned, the diplomatic foray will mark the first time that Kim, Russia's Vladimir Putin, and China's Xi Jinping appear at the same event.

On Monday, Xi and Putin took turns swiping at the West during a gathering of Eurasian leaders in Tianjin, just south of Beijing.

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The Shanghai Cooperation Organization (SCO) touts itself as a non-Western style of collaboration between 10 countries in the region and seeks to be an alternative to traditional alliances.

Kim's upcoming presence "formalizes the China-Russia-North Korea trilateral [relationship] to the public," Soo Kim, a geopolitical risk consultant and former CIA analyst, told AFP.

Kim enjoyed a brief bout of high-profile international diplomacy from around 2018, meeting US President Donald Trump and then South Korean President Moon Jae-in multiple times. He then withdrew from the global scene after the collapse of a summit with Trump in Hanoi, Vietnam, in 2019.

Kim stayed in North Korea throughout the Covid-19 pandemic, but ventured to Russia for a meeting with Putin in 2023.