BEIJING — A flurry of activity and speculation surrounding Beijing’s diplomatic quarter on Tuesday accompanied what officials described as an unusual, and highly secretive, visit by North Korea’s youthful leader, Kim Jong-un.

The prospect of a high-level visit from North Korea — including a meeting with China’s leader, Xi Jinping — raised questions about what Mr. Kim hopes to accomplish with this latest, unexpected burst of diplomacy after years of provocative threats punctuated by nuclear and ballistic missile tests.

A debut as an international statesman

Mr. Kim, while educated in Switzerland, had never previously traveled abroad since becoming North Korea’s leader in 2011. Nor has he met another head of state.

A visit to Beijing could capitalize on the relative success of North Korea’s diplomacy around the Winter Olympics in Pyeongchang, South Korea, last month.