By Christine Kim and Jeff Mason
SEOUL/WASHINGTON (Reuters) - World leaders welcomed prospects for a possible thaw in the long standoff over North Korea's nuclear weapons program on Friday after U.S. President Donald Trump said he was prepared to hold an unprecedented meeting with North Korean leader Kim Jong Un.
Trump and Kim prompted jitters around the world last year as they exchanged bellicose insults over the North's attempts to develop a nuclear weapon capable of hitting the United States. Pyongyang has pursued its nuclear program in defiance of U.N. Security Council resolutions.
But tension eased around last month's Winter Olympics in South Korea, laying the groundwork for what would be the first meeting between leaders from North Korea and the United States, and the biggest foreign policy gamble for Trump since he took office in January last year.
"A meeting is being planned," Trump said on Twitter after accepting an invitation to meet from Kim. There is no date or venue yet for the meeting although it could take place in May.
A senior State Department official said the talks would likely only be a preliminary discussion about holding future negotiations.
"The expectation is that the talks would lead to a discussion around a conclusion that we're ready to engage in negotiations," the official said.
News of the planned meeting was welcomed by China, which is North Korea's largest trading partner and its sole major ally, though overall trade has fallen in recent months as U.N. economic sanctions take effect.
President Xi Jinping told Trump in a phone call on Friday that he appreciates his desire to resolve the North Korea issue politically, Chinese state media said.
Xi "hopes the United States and North Korea start contacts and dialogue as soon as possible and strive to reach positive results,” the report added.
The head of South Korea's National Security Office, Chung Eui-yong, speaking in Washington on Thursday after briefing Trump about a meeting South Korean officials held with Kim this week, said Trump had agreed to meet the North Korean leader by May in response to Kim's invitation.
Kim had "committed to denuclearization" and to suspending nuclear and missile tests, Chung said.
Neutral Switzerland, which often hosts summits, said it was ready to facilitate the meeting.
Sweden could also play a role. North Korean Foreign Minister Ri Yong Ho will visit Sweden in the near future, Swedish newspaper Dagens Nyheter reported on Friday, quoting sources. The Swedish foreign ministry declined comment.
Sweden's embassy in Pyongyang represents U.S. interests, in the absence of U.S. diplomatic relations.
INSULTS AND THREATS
A Trump-Kim summit would be a major turnaround after a year in which North Korea has carried out a battery of missile tests that Washington sees as provocative and after a barrage of insults between the two leaders.
U.S.-based experts say North Korea appeared to show last November that it has succeeded in developing a missile capable of delivering a nuclear weapon anywhere in the United States.
Trump has derided Kim as a "maniac," referred to him as "little rocket man" and threatened in a speech last year to "totally destroy" North Korea, a country of 26 million people, if it attacked the United States or one of its allies.
Kim responded by calling Trump a "mentally deranged U.S. dotard."
The Trump administration has led a worldwide push to tighten international sanctions on North Korea to choke off resources needed for its weapons programs.
U.S. officials say the moves, which include restrictions on fuel supplies to North Korea, on its key coal exports, and to cut revenues it has received from tens of thousands of workers overseas, have begun to show signs of working.
North Korea sees a Trump meeting as a chance to win relief from the sanctions as well as an opportunity to earn the international legitimacy that it seeks, the U.S.-based Council on Foreign Relations think tank said.
"For Kim, the prospect of an early summit with Trump provides the best prospect of removing international sanctions pressure while giving Kim room for maneuver to possibly keep his nuclear deterrent in place," it said.
Vice President Mike Pence said the United States had made "zero concessions" and had "consistently increased the pressure" on North Korea.
Some U.S. officials and experts worry North Korea could buy time to build up and refine its nuclear arsenal if it drags out talks with Washington.
The government of Japan remained cautious about the talks.
Prime Minister Shinzo Abe and Trump, in a phone call, promised to continue to enforce sanctions until Pyongyang took "tangible steps ... toward denuclearization," the White House said in a statement.
A leading Democratic lawmaker said the Republican president would need help from others in the U.S. government if he is to go head-to-head with Kim over such complex issues as nuclear weapons and geostrategy.
"It will require the President to rely on the expertise within the State Department, the Intelligence Community, and throughout the government, and not simply on his own estimation of his skills as a ‘deal maker.’" Adam Schiff, the top Democrat on the House of Representatives Intelligence Committee, said in statement.
Trump had agreed to meet Kim without any preconditions, a South Korean official said.
"Kim Jong Un talked about denuclearization with the South Korean Representatives, not just a freeze," Trump said on Twitter on Thursday night. "Also, no missile testing by North Korea during this period of time. Great progress being made but sanctions will remain until an agreement is reached."
Trump's aides have been wary of North Korea's diplomatic overtures because of its history of reneging on international commitments and the failure of efforts on disarmament by previous U.S. administrations.
North and South Korea, where the United Sates stations 28,500 troops, are technically still at war after their 1950-53 conflict ended in a ceasefire, not a truce.
(Reporting by Christine Kim in Seoul, and Jeff Mason, David Brunnstrom, Matt Spetalnick, Steve Holland, Yara Bayoumy and John Walcott in Washington; Additional reporting by Lesley Wroughton and Susan Heavey in Washington, Kaori Kaneko in Tokyo and Ben Blanchard in Beijing; Writing by Alistair Bell; Editing by Paul Tait, Nick Macfie and Frances Kerry)