South Korean President Moon Jae-in said Friday North Korea understands the need to give up its existing nuclear weapons to achieve complete denuclearization and says it will do so. The only remaining questions are when and how, he added.

"North Korea promised complete denuclearization. It said it will give up nukes for economic development. (It) promised that it has no reason whatsoever to possess nukes while facing difficulties, such as sanctions, as long as the safety of their regime is guaranteed," Moon said in an interview with Britain's BBC news.

The interview was conducted one day before the South Korean leader was set to embark on his first trip to Europe that will take him to France and to Italy for the biennial Asia-Europe Meeting summit.

Moon said the complete denuclearization that North Korean leader Kim Jong-un promised included giving up existing weapons when asked.

"Complete denuclearization that Chairman Kim Jong-un says starts from not staging additional nuclear tests or nuclear missile tests and goes to dismantling facilities that produce nuclear weapons and develop missiles," the president said, according to a script of the interview released by his office Cheong Wa Dae.

"And it includes everything else, such as getting rid of existing nuclear weapons and nuclear materials," he added.

Moon has held three bilateral meetings with the reclusive North Korean leader, the most recent of which was their summit held in Pyongyang last month.

The president said he and the North Korean leader did not discuss when and how the North will completely give up its nuclear ambition, adding such issues need to be discussed between North Korea and the US.

"That is because North Korea is demanding the US take corresponding measures," he said.

Moon has long insisted that corresponding measures for the North's denuclearization steps should include declaration of a formal end to the Korean War, which he says may provide some security assurance to the North while also reducing the possibility of future conflicts on the Korean Peninsula.

The two Koreas technically remain at war as the 1950-53 war ended only with an armistice, not a peace treaty.

The US was earlier viewed as reluctant to give any reward to Pyongyang until the communist state fully denuclearizes.

Moon said the US has agreed to the need to formally end the Korean War, even before complete denuclearization of North Korea.

"The issue of declaring a formal end to the war has been widely discussed with the US side, including President (Donald) Trump. There was a consensus between South Korea and the US that it would be desirable for that to take place at the earliest date possible," he said.

"And therefore, I believe the declaration of a formal end to the war is only a matter of when and that it will certainly take place," the president added.

Moon's remarks, however, come shortly after the US president expressed his apparent opposition to easing sanctions on the North, at least for now, saying South Korea will not do so without US approval.

The South Korean president said Trump may have been stressing the need to maintain joint efforts and cooperation to denuclearize North Korea.

"The South-North Korean relationship requires separate efforts for improvement, but we plan to take efforts to improve South-North Korea relations within the boundaries of international sanctions as well, only to an extent that they will not violate those sanctions," he said.

The president stressed the need for the North to take actual denuclearization steps before his country or the international community could start considering removing their sanctions on the impoverished North.

"I believe North Korea must move forward actual denuclearization steps to enable such a condition. UN sanctions, as you may know, have intensified amid North Korea's continued provocations. I believe if North Korea continues to take sincere denuclearization steps and when it is believed to have reached a point of no return, the UN sanctions may start to be eased," he said.

Moon's three historic summits with Kim have led to an unprecedented level of rapprochement between the two Koreas, and they have agreed never to use military force against each other in a de facto non-aggression pact signed at the third Moon-Kim meeting in Pyongyang.

The Koreas have also launched a number of joint studies to gauge the possibility of economic cooperation in various areas, including railways, forestry and fisheries.

President Moon said his country's economic assistance or support for the impoverished North will begin when and if the international sanctions are removed or at least eased, but that giving the North a taste of what its denuclearization could bring will help further accelerate the process.

"Economic cooperation between the South and the North can be possible when these sanctions are removed or when inter-Korean economic cooperation is exceptionally allowed," Moon said.

"That is why we are saying we need to make preparations for economic cooperation in advance. They include joint researches or joint studies, as well as discussions on future cooperation. I believe they, on the other hand, may be meaningful in clearly showing North Korea that economic prosperity or a very bright future of North Korea may be guaranteed when North Korea makes the right choice, which is complete denuclearization," he added. (Yonhap)