"For President Moon Jae-in, he would like to see a substantial improvement in relations between the U.S. and North Korea by serving as a mediator," said Kim Yong-hyun, a professor at Dongguk University in Seoul.

The U.S. has demanded the complete dismantlement of the North's nuclear arsenal before reducing sanctions. Pyongyang wants a more step-by-step approach that would likely provide some sanctions relief for freezing its current nuclear capabilities.

The leaders from North and South Korea are also expected to endorse pursuing a peace treaty to replace the 1953 armistice to end the Korean War, but such a measure will require the participation of the U.S. and China as signatories to the truce.

Within the DMZ, security was tight Thursday, the day before the summit. About 2,800 journalists have registered at the main press center to cover the event.