Beijing has key strategic interests when it comes to North Korea, and has long feared that a collapse of its isolated neighbour could push waves of refugees into northeastern China, or that nuclear war on the Korean peninsula could contaminate swathes of the country.
The statement comes just hours after Trump and Kim's historic summit on North Korean nuclear weapons. "From reading this document, I don't think the U.S. will be successful".
Trump called Kim a worthy negotiator and plans to invite him to the White House in the near future.
North Korea also insists that the USA troop presence in the South, as well as its nuclear "umbrella" over allies Seoul and Tokyo, are part of America's "hostile" policy toward the North.
His statement was quickly portrayed by critics as a major, unreciprocated concession to a country that only past year was threatening Seoul and Washington with nuclear war.
Even a much derided 2005 joint statement - an early stage effort to launch more detailed talks, and therefore comparable to Tuesday's document - was more specific, according to Daryl Kimball, executive director of the Washington-based Arms Control Association.
What exactly did North Korea get out of the deal? Tuesday's statement made no mention of inspectors. However, Trump said North Korea sanctions would remain in place - for now. In its statement on the Singapore summit provided to The Daily Beast, the Department of Defense sidestepped the question, claiming USA "alliances remain ironclad, and ensure peace and stability in the region". Under the circumstances we are negotiating a complete deal", Trump said, adding "It is inappropriate to have war games.
The extensive and - by North Korean standards - fast coverage by the North also suggested an attempt to set the post-summit narrative of the vaguely worded declaration signed by Kim and Trump.More news: E3 2018 EA Play Press Conference Round-Up
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The agreement lacks details and a timetable on denuclearization.
Moon however cautioned that this was "just a beginning and there may be many difficulties ahead".
"President Trump committed to providing security guarantees to the DPRK and Chairman Kim Jong-un reaffirmed his firm and unwavering commitment to complete denuclearisation of the Korean Peninsula".
"When Trump spoke in Quebec he only referred to a possible agreement on long range missiles".
Following the talks, Second Deputy Chief of the Presidential National Security Office Nam Gwan-pyo said it was "significant" that the two leaders had learned to trust each other as partners to resolve issues through dialogue.
"It was a positive sentiment for a photo op, but it is not meaningful progress from past agreements, " he said, speaking in Singapore.
He added, "While Mr. Trump provides the background, I want [the government] to win a firm commitment from North Korea that a Japan-North Korea summit meeting will be held". Still, he offered no indication he planned to give up his arsenal, which he has called a "treasured sword". But the joint exercises, which the USA has described as a security and peacekeeping measure, have always been a sticking point; North Korea, which views the exercises as practice for an invasion, had threatened to cancel the summit over them.
"I can tell you definitively he did not, they had no idea this was coming", he said. "I look forward to further comment and clarification from the president when he gets here".