Donald Trump's high stakes pledge to make a deal over North Korea's nuclear weapons abruptly fell apart on Thursday, leaving the US president empty-handed and exposed to criticism that he had overplayed his hand and underestimated Kim Jong-un's will in negotiations. Two days of meetings in Hanoi ended prematurely with Mr Trump saying the North's leader had wanted sanctions lifted before taking steps to give up its atomic arsenal. The White House had planned “a joint agreement signing ceremony” but it, and a lunch between the two leaders, never took place. The US president boarded Air Force One and flew back to Washington. “Sometimes you have to walk and this was just one of those times,” Mr Trump said. “It was all about the sanctions. Basically, they wanted the sanctions lifted in their entirety, and we couldn't do that.” South Korea's stock market fell heavily and Japan's Prime Minister Shinzo Abe, in a phone call with Mr Trump, indicated that he should be the next world leader to meet Mr Kim. That exchange indicated that for progress to be made on denuclearization, other countries may now have to get involved given that Mr Trump's big talk had fallen flat. Christopher Hill, a retired US ambassador to South Korea who led a past US attempt to rein in Pyongyang's nuclear apparatus said the empty outcome in Hanoi indicated a lack of preparation. "It speaks to the fact that the Trump administration has not mastered the art of the deal or the basics of diplomatic tradecraft," Mr Hill told <em>The National</em>. “They need to regroup and learn from this mistake. It's obvious that Russia and China are not amused about being left on the sidelines and I don't think we are going to make progress without those two countries.” The United Nations and the US increased sanctions on North Korea when the reclusive communist state undertook nuclear and ballistic missile tests in 2017, adding to an already dire financial situation for Mr Kim's dictatorship. Against the odds and after threats to unleash “fire and fury” against Pyongyang, however, the US president and Mr Kim met in a landmark first summit in Singapore last June where they signed a vague pledge on denuclearisation. The Hanoi meeting was meant to boost that early diplomatic effort. Instead, it may have left it back at square one. “No deal is a surprise, especially as they were both all smiley last evening,” said Lim Soo-ho, senior research fellow at the Institute for National Security Strategy, in Seoul. “It means stakes were way too high for the two leaders to give another wishy-washy statement like they did in Singapore.” North Korea has not conducted any missile tests in almost 16 months and Mr Trump said there were discussions in Hanoi about the dismantling of the North's main nuclear complex at Yongbyon, but Mr Kim was not willing to do without sanctions relief first. The US president, accompanied by Secretary of State Mike Pompeo, said there were other demands that Washington had made. “We asked him to do more and he was unprepared to do that, but I'm still optimistic,” Mr Pompeo told reporters. The US had in recent days played down expectations of any breakthrough in Hanoi, though Mr Trump repeatedly dangled the prospect of North Korea becoming “an economic powerhouse” if it disarmed. However, American intelligence agencies have publicly warned that there is no sign that Pyongyang would surrender its estimated 30 nuclear weapons, which Mr Kim and his inner circle have long considered vital to its survival. Mr Hill, who served as an ambassador under Republican and Democratic administrations and now an academic at the University of Denver, said the State Department had to review its tactics. There should be no more summits with North Korea until preparatory work is done, he said, also reserving some criticism for Mr Pompeo. “He has a little of the Trump about him,” said Mr Hill of the US secretary of state. “He says things that are contradicted by the facts, but he should focus on the job of diplomacy rather than just pleasing the boss.”