A second summit between U.S. President Donald Trump and North Korean leader Kim Jong-un collapsed on Thursday over sanctions against Pyongyang. The two sides gave conflicting accounts of what happened, raising questions about the future of their denuclearisation negotiations.

"I believe this is part of a process to reach a higher level of agreement. Now our role has become even more important," South Korean President Moon said in a speech while commemorating a national holiday.

"My administration will closely communicate and cooperate with the United States and North Korea so as to help their talks reach a complete settlement by any means," he said.

Moon also said South Korea would consult with the United States on ways to resume tourism in Mount Kumgang and the operation of the Kaesong industrial complex, both in North Korea.

South Korea suspended operations at the jointly run factory park in Kaesong after a long-range rocket launch by Pyongyang in 2016, cutting off an important source of revenue for the impoverished North.

North Korea's Kim has also emphasised the need to bolster tourism as part of his drive to develop the country's economy.

The North earned $30 million annually from Mt. Kumgang tours between 1998-2008 before they were suspended, the South's unification ministry estimated.

Moon said South Korea's cooperation with Japan would also be strengthened for the sake of peace on the Korean peninsula.

"When the pain of victims is substantively healed through concerted efforts, Korea and Japan will become genuine friends with heart-to-heart understanding," Moonsaid, without giving specifics.

Relations between South Korea and Japan have soured since last year, when South Korea disbanded a fund meant to settle compensation for South Korean women forced to work in Japanese military brothels during World War Two.

South Korea's top court also ordered Japanese firms to compensate South Koreans for their forced labour in the war.