"The two leaders had conversations at length, enhanced mutual understanding and built more trust," Moon said in a speech commemorating the 100th anniversary of the March 1 Movement against Japanese colonial rule.

Both North and South Korea are united in their shared resentment of Japan's brutal 1910-45 colonial rule over the peninsula.

The no deal outcome from Hanoi will have been a huge disappointment for the South Korean president, who brokered the talks process and had touted the summit as a "remarkable breakthrough" for peace negotiations on the Korean peninsula.

Moon had been set to unveil details of new economic cooperation between the two Koreas this week, and now faces major questions over his dovish approach, but signalled he would not change track.

Seoul would consult with the US on ways to resume South Korean tourism to the North's Mount Kumgang and operations at the Kaesong Industrial Complex, where Southern firms used to be staffed by Northern workers, he said.

Moon has been pushing for the resumption of both projects as he seeks to engage Pyongyang, but doing so would fall foul of sanctions imposed on the North since they were suspended.

A joint North-South economic committee would be set up to benefit both sides "when there is progress in denuclearisation", he added, and said unification of the two Koreas "need not be far away".

But after 70 years of division the two are now radically different societies and the South is far wealthier than the North.

Despite Moon's optimism, some in South Korea said they did not foresee any more US-North Korea summits.

"It seems like there isn't much left to talk about," said Kim Seong-min, president of Free North Korea Radio, a private broadcaster led by North Korean defectors in Seoul.

"Unless Kim changes his mind and really decides to give up all nuclear weapons and facilities, not just Yongbyon. But that's unlikely."