By Hyonhee Shin and John Walcott
SEOUL/WASHINGTON (Reuters) - North Korea pledged to roll back some of its missile programme on Wednesday, drawing an enthusiastic response from U.S. President Donald Trump, even though some U.S. officials and experts fear a ploy to weaken Washington's resolve and its alliance with Seoul.
In a joint statement after a summit with South Korean President Moon Jae-in in Pyongyang, North Korean leader Kim Jong Un pledged to permanently abolish North Korea's key missile facilities in the presence of foreign experts.
He said he was also willing to close the country's main nuclear complex - but only if the United States took unspecified reciprocal action.
Trump welcomed Kim's pledges, calling them part of "tremendous progress" with Pyongyang on a number of fronts, and hailing "very good news" from the summit between the Koreas.
"He's calm, I'm calm - so we'll see what happens," Trump told reporters, referring to Kim, who he met at an unprecedented summit in Singapore in June.
"It's very much calmed down," added Trump, who last year engaged in a heated war of rhetoric with Kim in which he threatened to totally destroy North Korea.
Analysts said Kim's pledges could inject fresh momentum into stalled nuclear negotiations between Washington and Pyongyang and lay the groundwork for another Kim-Trump meeting.
But two senior U.S. officials involved in U.S. North Korea policy said the Moon-Kim summit had reinforced fears of some within the Trump administration of an easing of pressure on North Korea to give up its nuclear weapons, and a weakening of the longstanding U.S. alliance with South Korea.
At the summit, the two Koreas agreed to plans to resume economic cooperation, including working to reconnect rail and road links. They also agreed to restart a joint factory park in a border city and tours to the North's Mount Kumgang resort.
Experts said the projects could constitute a violation of U.S.-driven U.N. Security Council sanctions aimed at drying up resources for Pyongyang's weapons programs.
The U.S. officials, who spoke on condition of anonymity, expressed concern about what appeared to be an attempt by Kim to drive a wedge between Washington and Seoul, and one said Moon's agreement to create a 10 km (six mile) buffer zone along the demilitarized zone dividing the Koreas could erode the readiness of U.S. and South Korean forces.
The official said that by pledging to destroy the Dongchang-ri missile site, which North Korea has used to develop inter-continental ballistic missiles, Kim appeared to be trying to create space for Trump to claim that he had ended the North Korean threat to the United States, and even the danger of war on the Peninsula, something that "would remove the grounds for the military alliance with Seoul."
Trump has questioned the rationale and cost of keeping 28,500 U.S. troops based in South Korea. Pyongyang has long sought their withdrawal.
The second official said it was not clear what reciprocal action Washington was supposed to take, leaving Kim room to claim that Washington had not done enough for North Korea to follow through on its pledges.
Even if North Korea were to shut down its Yongbyon nuclear test site, officials and experts believe it has other secret nuclear facilities it can employ.
Melissa Hanham, a non proliferation expert at the Middlebury Institute of International Studies in California, said North Korea could use mobile launchers to test ICBMs even if it shut down Dongchang-ri.
'NO CLOSER TO DISARMAMENT'
Speaking at a joint news conference in Pyongyang, the two Korean leaders agreed to turn the Korean peninsula into a "land of peace without nuclear weapons and nuclear threats."
Kim pledged to work towards the "complete denuclearisation of the Korean peninsula" during two meetings with Moon earlier this year and at his summit with Trump in Singapore.
But discussions over how to implement the vague commitments have since faltered and North Korea has consistently refused to give up its nuclear arsenal unilaterally.
Vipin Narang, an associate professor of political science at the Massachusetts Institute of Technology, tweeted that the Moon-Kim summit had made the Korean peninsula safer.
"But it is no closer to North Korean disarmament," he said.
Washington has demanded concrete action towards denuclearisation, such as a full disclosure of North Korea's nuclear and missile facilities, before agreeing to key goals of Pyongyang, including an easing of international sanctions and an official end to the Korean War.
Though North Korea has unilaterally stopped nuclear and missile tests in the past year, it did not allow international inspections of the dismantling of its main 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 at Dongchang-ri, according to Kim and Moon's joint statement.
Kim also said he would visit Seoul in the near future, in what would be the first-ever visit to South Korean capital by a North Korean leader.
The two Koreas also agreed to pursue a bid to co-host the 2032 Summer Olympic Games.
South Korea's national security adviser, Chung Eui-yong, said the reciprocal U.S. steps could include an end-of-war declaration. The South Korea and the United States remain technically at war with North Korea because the 1950-53 Korean War ended in armistice and not a peace treaty.
North Korea has consistently refused to give up its nuclear arsenal unilaterally, and stressed that Washington should first agree to formally end the war.
Satellite images and other evidence in recent months have suggested North Korea is continuing to work on its nuclear programme clandestinely.
Kim's latest promises come days before Moon meets Trump at the U.N. General Assembly in New York next Monday.
South Korean officials hope Moon will be able to convince Trump to restart nuclear talks with Pyongyang, after he cancelled a trip to North Korea by Secretary of State Mike Pompeo last month, citing lack of progress.
Senior voices in the U.S. Congress have expressed scepticism about the Kim-Moon talks.
Republican Senator Lindsey Graham said on Tuesday that North Korea had not moved towards denuclearisation and the summit risked undermining the U.S. sanctions campaign
Democratic Senator Edward Markey welcomed the talks, but also highlighted the lack of progress towards North Korean denuclearisation, saying in a statement that Kim had doubled down on "deceive and delay."
(Reporting by Hyonhee Shin, Joyce Lee, Soyoung Kim and Joint Press Corps; Additional reporting by Jeongmin Kim, Haejin Choi and Ju-min Park in Seoul, and Roberta Rampton, David Brunnstrom and John Walcott in Washington; Editing by Alex Richardson and Alistair Bell)