Kim met South Korean President Moon Jae-in at the border truce village of Panmunjom, in the highlight of a diplomatic whirlwind that has swept the flashpoint peninsula.

In a joint declaration, they "confirmed the common goal of realising, through complete denuclearisation, a nuclear-free Korean peninsula".

Moon hailed the declaration as a "precious start" for denuclearisation of the peninsula -- a diplomatic euphemism open to interpretation on both sides.

Pyongyang has long wanted to see an end to the US military presence and nuclear umbrella over the South, but it invaded its neighbour in 1950 and is the only one of the two Koreas to possess nuclear weapons.

Koo Kab-woo, professor at the University of North Korean Studies, told AFP the declaration was "much stronger than what I expected".

"It mentions complete denuclearisation, which sends a positive signal to the US," he said.

But analysts say it remains to be seen whether the vague statement will lead to more concrete steps toward denuclearisation.

The declaration was a "necessary but not sufficient step", said Daniel Pinkston, a North Korea expert at Troy University in the United States.

"Everything will turn on follow-up, details and implementation," he added. "There is a very long way to go."

Pyongyang announced last week a moratorium on atomic and intercontinental missile tests -- a move that met with scepticism from some analysts who argued the North may see little need to further test its proven weapons capability anyway.

And the North has declared moratoriums before and talked about denuclearisation, while previous agreements have ultimately floundered, with Pyongyang making rapid progress in its capabilities under Kim.

Since inheriting power from his father in 2011 Kim has overseen four of the country's sixth atomic tests and last year presided over launches of missiles capable of reaching the US mainland, before declaring the development of its arsenal complete.

"Is Kim really willing to abandon the nuclear programme he has so heavily invested in" asked Paul Haenle, director of the Carnegie-Tsinghua Center for Global Policy. Or will he "be more likely try to seek an agreement not to develop beyond his current capabilities?"

Washington is demanding Pyongyang completely give up the weapons it has spent decades developing and which Kim has hailed as a "treasured sword" to protect the North from a US invasion.

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Kim and Trump are expected to meet in the coming weeks at a venue yet to be decided -- Mongolia and Singapore are reportedly the favourites -- after Moon seized on the Winter Olympics in the South to broker dialogue between them.

Whether Friday's broad declaration will ultimately produce tangible progress will depend on the outcome of the North-US summit long sought by Pyongyang, said Christopher Green, analyst at the International Crisis Group.

"Denuclearisation is a matter for the United States and North Korea," he told AFP.

Koh Yu-hwan, a professor of North Korean Studies at Dongguk University, added: "To be frank, in (the) South-North summit, denuclearisation is more like a word-for-word commitment.

"Action-for-action, specific process and measures must be discussed at the US-North Korea summit."

But some analysts were sceptical of the prospects on both sides. "We've heard/seen this before," tweeted former State Department official and Hillary Clinton aide Laura Rosenberger.

Kim was still in the "driver's seat", she said, which boded ill for the next stage as Trump was "eager for a win, and KJU has learned how to play him with hollow gestures".

And she added: "Also in all the coverage of hand-holding and hugs, let's not forget Kim's a brutal dictator."