"The world is focused on Chairman Kim's commitment to denuclearization," he said.

The trip comes shortly before Xi and US President Donald Trump travel to Osaka, Japan, for a Group of 20 summit, leading analysts to believe the Chinese leader is seeking to use his leverage on the North Korean nuclear issue as a bargaining chip in trade negotiations with the US.

Adding weight to the theory is the current stalemate in denuclearization negotiations between Washington and Pyongyang. No working-level talks have taken place since Trump and Kim abruptly ended their second summit in February without an agreement.

Trump said last week, however, that he had received another "beautiful" letter from the North Korean leader and that he was in no rush to strike a deal.

Asked about Kim's seriousness about dismantling his nuclear weapons and missile programs, US State Department spokeswoman Morgan Ortagus said both Trump and Secretary of State Mike Pompeo "believe" the North Korean leader will "fulfill his commitment to denuclearize."

"That remains our policy," she said at a press briefing.

Meanwhile, in separate remarks sent to Yonhap, a State Department spokesperson said the US will continue to closely coordinate with other countries, including China, to denuclearize the North.

"The United States along with our partners and allies, and other permanent members of the UN Security Council, including China, are committed to the shared goal of achieving the final, fully verifiable, denuclearization of North Korea," the spokesperson said.

"The United States and the international community have a shared understanding of what final, fully verified denuclearization entails and what meaningful progress toward that goal looks like."

Xi's trip to North Korea follows four visits by Kim to the neighboring country, which remains Pyongyang's sole major ally and trading partner.

The two countries have been seen renewing their traditionally close ties, which soured after China backed UN Security Council sanctions on North Korea over its nuclear weapons and intercontinental ballistic missile tests in 2017. (Yonhap)