US National Security Adviser Jake Sullivan met with his Chinese counterpart in Luxembourg on Monday, the White House said, calling the lengthy exchange between the rival powers "frank."The meeting between Sullivan and Yang Jiechi followed a phone conversation between the two on May 18 and lasted four and a half hours, a senior official told reporters.The two held "frank, substantive and productive discussions on a number of regional and global security issues, as well as key issues in US-China relations," the White House said in a statement.In the text, Sullivan emphasized "the importance of maintaining open lines of communication to manage the competition between our two countries."The official, who spoke to reporters on condition of anonymity, acknowledged disagreements and tensions between the two countries on a number of issues, including the US-led attempts to isolate Russia over its invasion of Ukraine and the Chinese threat to Taiwan.Just this Sunday, Chinese Defense Minister Wei Fenghe promised that his country will fight "until the end" and "at any cost" to stop any attempt at independence by this island with a democratic and autonomous government.At the meeting in Luxembourg, Yang Jiechi pointed out that the Taiwan issue "affects the political foundations" of their bilateral relations and that "if not handled properly, it will have a subversive impact," the official Chinese news agency Xinhua reported."The United States should have no misjudgments or illusions" about Taiwan, he added.During a visit to Japan last month, US President Joe Biden had said that the United States will defend this island in case of attack, a change from the traditional US policy of "strategic ambiguity" on this issue.Three issues stopped through the referendums in the votes in Switzerland on May 15.The aforementioned source said that Sullivan reiterated Washington's policy of recognizing Chinese sovereignty over Taiwan but expressed "concerns about Beijing's coercive and aggressive actions" towards the island.Despite the differences, dialogue is valued to "keep the lines of communication open," the official said."We think about it not necessarily in terms of specific agreements, but more in terms of ensuring that each side understands the intentions of the other, the priorities of the other," he said, adding that this "is crucial" to avoid misunderstandings and "reduce the risks".Relations between the two powers were strained during the previous administration of Donald Trump, who triggered a trade war in response to what he described as abusive practices by China.Biden says he is considering lifting some tariffs in a bid to quell rising inflation in the United States.SWI swissinfo.ch - business unit of the Swiss radio and television company SRG SSRYour data is used to fill in some fields of the form.A confirmation email has been sent to your mailbox.Click on the link included in the email to activate your account.Enter your email address.You will receive a link to reset your password.An email to reset your password has been sent to your mailbox.Please click the link in the e-mail to reset your password.