It warned the Trump-Kim summit could be in jeopardy, too.
South Korea and Japan are both market economies, democracies and United States allies, and both are threatened by nuclear-armed North Korea, but their relationship is heavily strained by historical and territorial issues.
But Chris Johnson, a former China analyst at the Central Intelligence Agency, said China was dealing with some "significant concerns" regarding the implications of the Trump-Kim summit.
Mr. Trump has said he wants quick action after the achievement of a four-point joint statement at the summit committing to the denuclearization of the Korean Peninsula and the pursuit of improved relations between Washington and Pyongyang - potentially toward the lifting US sanctions on North Korea.
He did not elaborate on what kinds of changes the U.S.is weighing, but the North has repeatedly taken umbrage with joint U.S.
The rapprochement on the Korean peninsula was triggered earlier this year when Kim made a decision to send athletes, cheerleaders and his sister as an envoy to the Pyeongchang Games.
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In a joint statement following the Singapore meeting, Kim pledged to "work toward the complete denuclearisation of the Korean Peninsula". Those priorities, from China's perspective, would be to ensure that Beijing is included in any in peace treaty talks and for creating an environment on the Korean Peninsula that will make it unnecessary for United States troops to remain.
For instance, discussions between Secretary of State Mike Pompeo and his North Korean counterpart over drawing a roadmap for denuclearization are being delayed. "The old prejudices and practices worked as obstacles on our way forward, but we overcame all of them and we are here today".
Following his summit with Mr Trump, Mr Kim was expected to meet with Chinese leaders to discuss progress in halting his country's missile and nuclear weapons programmes in exchange for economic incentives.
Trump's suspension plan has been stirring up heated debate, with supporters calling it a good-will gesture to facilitate the North's denuclearization and naysayers a blow to the bilateral alliance.
Moreover, almost 1 in 3 people saw the talks as successful for North Korea, while only 1 in 5 saw it as benefiting the United States, according to the poll.
Trump tweeted Monday that "if President Obama.had gotten along with North Korea" and taken steps toward peace "the Fake News would have named him a national hero!"