Leaders in Beijing are anxious, experts say, that Kim might try to counterbalance China's influence by embracing the US, North Korea's longtime enemy.
The key phrase in the agreement is that in exchange for security guarantees, Kim reaffirms his commitment to the denuclearization of the Korean Peninsula.
As Seoul sought clarification on the U.S. position towards its long-standing ally, USA secretary of State Mike Pompeo was travelling to South Korea to brief President Moon.
At the summit, Trump emphasized what North Korea has to gain by giving up its nuclear weapons and rejoining the global community - a subject he returned to on Twitter.
"Right now, the USA and South Korea are not engaged [on troop withdrawal], and we're the only ones who make up our mind on this", he said. If Washington does not bring back its military from South Korea, there will be no denuclearization. -North working-level talks from now on.
"North Korea has committed to a complete denuclearisation".
At a news conference before leaving the Singapore summit, Trump also speculated on the long-term possibility of withdrawing the 28,500 US troops in Korea if the initial agreement with North Korean leader Kim Jong Un leads to denuclearization and peace. Either way, a realignment in northeast Asia appears underway.
Trump said Tuesday that he would invite Kim to the White House at an "appropriate time".
"If this indeed kicks off a very rapid process of dialogue to begin eliminating their nuclear infrastructure, that would be something new, but the agreement does not provide for that".
On Monday, Mattis told Pentagon reporters that there had been no discussions on future withdrawals of US troops from Korea. -South Korea military exercises would make "some degree of sense" if North Korea had requested it and the US had agreed to do so as a signal of good faith, but noted that the concessions Washington received from Pyongyang at the summit were "almost non-existent".
"I don't know exactly what the timing will be for our next conversation with the North Koreans", Pompeo said.
North Korean state media lauded the summit as a resounding success, highlighting concessions made by the U.S. president.
While Japan is concerned about their citizens who were abducted decades ago by Pyongyang, the signed paper makes no specific reference to abductees in North Korea when referring to the repatriation of the remains of prisoners of war and people killed during fighting. But the sanctions cut North Korea's coal exports down to 4.8 million tonnes to China.
While South Korean stock investors lent considerable weight to the meeting between the two Korean leaders, they were less excited by this week's events in Singapore.
Pompeo said last week that he would discuss with his counterparts the next steps involving North Korea, in what he described as "an update and [to] underscore the importance of fully implementing all sanctions that are imposed on North Korea".
"We believe that this is the only correct direction for resolving the peninsula issue. I hope it will be eventually".
President Donald Trump has arrived back in Washington from his historic nuclear summit with North Korea's Kim Jong Un in Singapore.
But Morell says the U.S.is far from being able to claim a strategic victory, given the "immense details to work through".
Then his sister, Kim Yo-jong, gave him a different one to use at the last second. "In that sense, it might have been better if the summit was not held at all". The senator added that because of Trump's comments referring to the end of the exercises, "that's why I said there needs to be some clarification". Written in English by Joshua Lipes.