North Korea said it would permanently abolish its key missile facilities in the presence of foreign experts, the latest gesture by leader Kim Jong Un to revive faltering talks with Washington over his country's nuclear programme.

Speaking at a joint news conference in Pyongyang on Wednesday, Kim and South Korean President Moon Jae-in said they agreed to turn the Korean peninsula into a "land of peace without nuclear weapons and nuclear threats".

North Korea was also willing to close its main nuclear complex if the United States took unspecified "reciprocal action", they added.

The pledges Kim and Moon made at their third summit this year could inject fresh momentum into the stalled nuclear negotiations between Washington and Pyongyang and lay the groundwork for another meeting Kim recently proposed to U.S. President Donald Trump.

Kim pledged to work toward the "complete denuclearisation of the Korean peninsula" during his two meetings with Moon earlier this year and at his historic June summit with Trump in Singapore.

But discussions over how to implement the vague commitments have since faltered. Washington is demanding concrete action towards denuclearisation before agreeing to key goals of Pyongyang - declaring an official end to the 1950-53 Korean War and easing tough international sanctions.

Trump‏ called the latest pledges "very exciting".

"Kim Jong Un has agreed to allow Nuclear inspections, subject to final negotiations, and to permanently dismantle a test site and launch pad in the presence of international experts. In the meantime there will be no Rocket or Nuclear testing," Trump wrote on Twitter.

Kim said he will visit Seoul in the near future, in what would be the first-ever visit to the South's capital by a North Korean leader. Moon said the visit was expected to take place by the end of the year.

Verification

The latest pledges by Kim come days before Moon meets with Trump in New York on the sidelines of the U.N. General Assembly next week. Seoul officials hope Moon will be able to convince Trump to restart nuclear talks with Pyongyang, after he cancelled a trip by his secretary of state to Pyongyang last month, citing lack of progress.

Though North Korea has unilaterally stopped nuclear and missile tests, it did not allow international inspections for a dismantlement of its only known nuclear test site in May, drawing criticism that its action was for show and could be easily reversed.

As a next step, North Korea will allow experts from "concerned countries" to watch the closure of its missile engine testing site and launch pad in the northwestern town of Dongchang-ri, according to a joint statement signed by Moon and Kim. The facilities were a key test centre for its intercontinental ballistic missiles designed to reach the United States.

The North also "expressed its readiness" to take additional measures, such as a permanent dismantlement of its main nuclear facilities in Yongbyon should there be unspecified corresponding action from the United States.

Those U.S. steps could include an end-of-war declaration, South Korea's national security adviser, Chung Eui-yong, told reporters.

North Korea has consistently refused to give up its nuclear arsenal unilaterally, and stressed that a formal declaration to end the 1950-53 Korean War should come first.

"I don't think President Moon got everything he was seeking, but Kim gave Moon some tangible things for which he can take credit and some forward progress in terms of beginning a more substantive discussion and increased activity focused on denuclearisation," said Michael Madden, an analyst at the Stimson Centre's 38 North in Washington.

Satellite images and other evidence in recent months have suggested North Korea is continuing to work on its nuclear programme clandestinely.

The United States has so far failed to convince Pyongyang to declare an inventory of nuclear weapons, facilities and materials, or commit it to a specific timeline for denuclearisation.

"I think we should take these steps as very positive, but remember that North Korea is still taking baby steps," said Melissa Hanham, a senior research associate at the James Martin Centre for Nonproliferation Studies.

"We don't have a timeline, and we also don't have any guarantees about the larger nuclear and missile programmes."

Sanctions pressure

The two Koreas agreed to begin construction to reconnect railways and roads within this year. They will also work to restart a joint factory park in the North border city of Kaesong and tours to the North's Mount Kumgang resort, when conditions are met.

But some experts worry those projects could constitute a violation of U.N. Security Council sanctions aimed at drying up resources for Pyongyang's weapons programmes, and upset Washington.

Later on Wednesday, Moon's delegation is scheduled to tour the Mansudae Art Studio, the North's largest producer of art and propoganda, which was sanctioned by the United Nations last year.

The two Koreas also agreed to pursue a bid to co-host the 2032 Summer Olympic Games, and actively work together in other international competitions including the 2020 Olympic Games in Tokyo.

They also adopted a separate military accord aimed at preventing armed clashes between the old foes, which are technically still at war because the Korean War ended with a truce, not a peace treaty.

The neighbours will gradually withdraw guard posts and equipment in a move to transform the world's most heavily fortified border into a no-weapons area, the agreement said.

Later on Wednesday, Moon is scheduled to watch the North's signature "Brilliant Fatherland" Mass Game, with a formation of glowing drones, lasers and stadium-sized gymnastics shows designed to glorify the country.

On Thursday, the last day of his three-day visit, Moon plans to visit Mount Baektu in North Korea with Kim before returning home.

North Korea says Kim's grandfather and father were born at Mount Baektu, a centrepiece of the North’s idolization and propaganda campaign to highlight the ruling family's sacred bloodline.