President Moon Jae-in sought to rally public support for his upcoming dialogue with North Korean leader Kim Jong-un Thursday, saying it would require all-out efforts on all sides to ensure success in the rare opportunity to ease tension between the two Koreas.

"Now the South-North summit will be held in about half a month. A North-US summit is also scheduled to be held thereafter. They will be once-in-a-life time chance to completely denuclearize the Korean Peninsula, establish permanent peace and move toward sustainable development of South-North Korea relations," the president said while meeting with a group of 21 advisers, including his special security adviser Moon Chung-in.

"We must work to make the most of this opportunity," he added.

The meeting, held at the presidential office Cheong Wa Dae, came about two weeks before the South Korean president will meet the North Korean leader on April 27. It was attended by a number of North Korea experts, such as Lim Dong-won, a former unification minister who also headed the National Intelligence Agency.

"We must successfully hold the South-North summit so it will also lead to the success of the North-US summit, but none of them is an easy task," the president told the meeting, according to Cheong Wa Dae pool reports.

US President Donald Trump has said he will likely meet Kim in May or early June. The Trump-Kim meeting, if held, will mark the first-ever US-North Korea summit.

Moon also highlighted the importance of support from the people.

"The government will lead the way and communicate with the people, but I ask you elders, who are more persuasive than any others when it comes to South-North Korea relations, to help in any way you can to bring the people's minds together," he said.

The upcoming inter-Korean summit will mark the third of its kind after those held in 2000 and 2007, both in Pyongyang.

Moon noted his meeting with Kim may involve the toughest and most difficult negotiations so far, partly because of advances in the communist state's nuclear and missile development programs over the past decade.

"We have the experience of holding two South-North summits ... and were able to push for the upcoming summit because of such experience and results. But the current situation is more serious than any other time in the past. Military tension found a new peak while South-North relations remained ruptured over the past 10 years with North Korea's nuclear and missile technologies advancing to a point where even the US feels threatened," the president said, again underscoring the importance of positive outcomes from the US-North Korea summit.

"And that is why I say today that the experience and wisdom of you elders are more needed than ever to ensure not only the success of the South-North summit but also the success of the North-US summit," he added.

North Korea conducted its sixth and most powerful nuclear test so far in September. It has also staged nearly a dozen missile tests since Moon took office in May 2017. (Yonhap)