Chief among these include a peace treaty to formally end the Korean War, which is still in a state of truce after the 1953 armistice, a US troop withdrawal or reduction from the Republic of Korea, and a dramatic reduction of US-ROK joint military drills.

Shen doubted the US would do anything to reduce troops or military drills, but he said it might offer some legally bound security assurance to the DPRK.

Charles Armstrong, a professor of Korean Studies at Columbia University in New York, said it is not realistic to expect the DPRK to completely give up its nuclear program right away. He said the big question is whether the engagement can be sustained even if a major agreement is reached at the summit.

"No one wants to return to the dangerous confrontation of last year, and it is possible that the talks will fail and the US will return to a policy of ‘maximum pressure'," he said, while the DPRK "returns to provocative actions".

"There seems to be enough political will at the moment in Pyongyang, Seoul, Washington and Beijing to move the peace process forward, but there are many unforeseeable factors including especially domestic opposition in the US," Armstrong said.

The US Republican and Democratic parties have pressured Trump not to make too many concessions in talks with Kim.

Video: Singapore Prime Minister’s Office