(CNN) There is a strong possibility that North Korean leader Kim Jong Un is in Beijing, an official with deep knowledge of North Korea told CNN.

If Kim did in fact make the journey from Pyongyang to the Chinese capital, it would be the first time the young leader has left his home country since taking power after his father's death in 2011.

The visit comes weeks before Kim's planned summit with South Korean President Moon Jae-in and a potential meeting with US President Donald Trump.

The Kim family train is seen in Russia in 2011.

North Korea's relations with China, a traditional ally, have been strained since Kim purged several top-ranking officials close to Beijing, including his uncle, Jang Song Thaek. Tensions were heightened in 2017 after a string of missile tests, which rankled China's leaders and resulted in multiple rounds of United Nations sanctions targeting North Korea's ability to bring in cash.

However, a flurry of diplomacy this year, at first largely centered around North Korea's participation in the Winter Olympics in Pyeongchang last month, culminated in an announcement that Kim would meet with his South Korean counterpart in April and a planned summit with Trump by May.

The source close to North Korea told CNN that a high-level South Korean delegation implored Kim to meet with Trump during a visit to Pyongyang earlier this month.

Kim verbally agreed, but didn't think it would be publicized or happen so soon. He was even more surprised that the United States and South Korea made a big announcement, the source said.

Experts have noted that while China has publicly lauded peaceful efforts to resolve tensions on the Korean Peninsula, it ran the risk of being relegated to the sidelines.

Tong Zhao, a North Korea expert at the Carnegie Tsinghua Center for Global Policy in Beijing, said the visit may be geared toward enlisting China's support ahead of Kim's proposed summit with Trump and a back-up plan should diplomatic talks fail.

"North Korea wants to have some insurance against this upcoming summit meeting with President Trump ... the meeting is very important but also very risky," he said. "If the meeting fails, the US could declare that diplomacy has failed and shift to a more coercive approach or even a military strike."

China has a mutual defense treaty with North Korea under which both parties pledge to "immediately render military and other assistance by all means at its disposal" in the event of war or foreign attack, though some analysts have called into question whether Beijing would honor it.

More at https://edition.cnn.com/2018/03/27/asia/china-north-korea-train-intl/index.html