BEIJING/SEOUL - North Korean leader Kim Jong Un has pledged to denuclearize and meet US officials, China said on Wednesday after an historic meeting with President Xi Jinping, who promised China would uphold its friendship with its isolated neighbor.After two days of speculation, China and North Korea both confirmed that Kim had visited Beijing and met Xi during what China's Foreign Ministry called an unofficial visit to China from Sunday to Wednesday.The China visit was Kim's first known trip outside North Korea since he assumed power in 2011 and is believed by analysts to serve as preparation for upcoming summits with South Korea and the United States.North Korea's KCNA news agency made no mention of Kim's pledge to denuclearize, or his anticipated meeting with US President Donald Trump that is planned for some time in May.Beijing has traditionally been the closest ally of secretive North Korea, but ties have been frayed by Pyongyang's pursuit of nuclear weapons and China's backing of tough UN sanctions in response.China's Foreign Ministry cited Kim in a lengthy statement as telling Xi that the situation on the Korean peninsula was starting to improve because North Korea had taken the initiative to ease tensions and put forward proposals for peace talks."It is our consistent stand to be committed to denuclearization on the peninsula, in accordance with the will of late President Kim Il Sung and late General Secretary Kim Jong Il," Kim Jong Un said, according to the statement. North Korea is willing to talk with the United States and hold a summit between the two countries, he said."The issue of denuclearization of the Korean Peninsula can be resolved, if South Korea and the United States respond to our efforts with goodwill, create an atmosphere of peace and stability while taking progressive and synchronous measures for the realization of peace," Kim said.NUCLEAR UMBRELLAKim Jong Un's predecessors, grandfather Kim Il Sung and father Kim Jong Il, both publicly promised not to pursue nuclear weapons but secretly continued to develop the programs, culminating in the North's first nuclear test in 2006 under Kim Jong Il.The North had said in past failed talks aimed at dismantling its nuclear program that it could consider giving up its arsenal if the United States removed its troops from South Korea and withdrew its so-called nuclear umbrella of deterrence from South Korea and Japan.Many analysts and former negotiators believe this still constitutes North Korea's stance on denuclearisation of the Korean peninsula and remain deeply skeptical Kim is willing to give up the nuclear weapons his family has been developing for decades.At first wrapped in secrecy, the announcement of Kim Jong Un's visit soon became the third-most discussed topic on China's Twitter-like Weibo microblogging site, although many state media outlets blocked their comments sections.Widely read Chinese state-run newspaper the Global Times praised the meeting as proving naysayers about Beijing-Pyongyang relations wrong. "China and North Korea maintaining their friendly relations provides a positive force for the whole region and promotes strategic stability in northeast Asia," it said in an editorial.Billed as an unofficial trip, Kim's appearance in Beijing contained almost all the trappings of a state visit, complete with an honor guard and banquet at Beijing's Great Hall of the People.Kim and Xi also met at the Diaoyutai State Guest House, where Kim Il Sung planted a tree in 1959 that still stands.State television showed pictures of the two men chatting amiably and Kim's wife, Ri Sol Ju, getting an equally warm welcome from Xi's wife, Peng Liyuan.TRUMP BRIEFEDChina briefed Trump on Kim's visit and the communication included a personal message from Xi to Trump, the White House said in a statement."The United States remains in close contact with our allies South Korea and Japan. We see this development as further evidence that our campaign of maximum pressure is creating the appropriate atmosphere for dialog with North Korea," the statement said.A top Chinese diplomat, Politburo member Yang Jiechi, will brief officials, including President Moon Jae-in, in Seoul on Thursday about Xi's meeting with Kim Jong Un, according to the presidential office in Seoul.Kim told a banquet hosted by Xi the visit was intended to "maintain our great friendship and continue and develop our bilateral ties at a time of rapid developments on the Korean peninsula," according to KCNA.Xi had accepted an invitation "with pleasure" from him to visit North Korea, KCNA said.However, China's statement made no mention of Xi accepting an invitation, saying only that Xi pledged to keep frequent contacts with Kim through the exchange of visits and sending special envoys and letters to each other.China had largely sat on the sidelines as Pyongyang improved its relations with Seoul, prompting worry in Beijing that it was no longer a central player in the North Korean issue, reinforced by Trump's subsequent announcement of his proposed meeting with Kim Jong Un in May."China is North Korea's lifeline, so the notion, from a Chinese perspective, that Kim Jong Un couldn't have these other two meetings before meeting with Xi Jinping, I think the Chinese just thought that is not going to happen," said Paul Haenle, director of the Carnegie–Tsinghua Center in Beijing and the former White House representative to North Korea denuclearization talks from 2007-2009.Improving ties between North Korea and China would be a positive sign before the planned summits involving the two Koreas and the United States, a senior South Korean official said on Tuesday.Kim Jong Il met then-president Jiang Zemin in China in 2000 before a summit between the two Koreas in June that year. That visit was seen at the time as reaffirmation of close ties with Beijing.Speculation about a possible visit by Kim Jong Un to Beijing was rife earlier this week after a train similar to the one used by his father was seen in the Chinese capital, along with heavy security and a large motorcade.The secrecy around the visit was not unusual. The later visits of Kim Jong Il to China were only announced by both countries once he had left the country.