President Trump escalated his war of words with North Korean leader Kim Jong Un on Tuesday evening, asserting that his "nuclear button" is "much bigger & more powerful" than the North Korean leader's and threatening that the U.S. arsenal "works." 
 
 Trump was responding to Kim's annual New Year's Day speech on Monday, during which the North Korean leader boasted that the United States is "within the range of our nuclear strike and a nuclear button is always on the desk of my office." 
 
 Trump said in his Tuesday tweet, "North Korean Leader Kim Jong Un just stated that the 'Nuclear Button is on his desk at all times.' Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!" 
 
 North Korean Leader Kim Jong Un just stated that the “Nuclear Button is on his desk at all times.” Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works! — Donald J. Trump (@realDonaldTrump) January 3, 2018 
 
 The exchange represents a ratcheting up of rhetoric, after Trump in recent months had adopted a measured approach to North Korea — relative to last summer, when he warned of "fire and fury" — at the urging of his national security team. 
 
 Earlier Tuesday, however, Trump revived his derisive nickname for Kim — "rocket man" — in response to signs of relaxed tensions between South Korea and North Korea. South Korea agreed to an offer from North Korea for the two countries to talk ahead of next month's Winter Olympic Games in PyeongChang, South Korea. Kim said in his Monday address that he was willing to send a delegation of North Korean athletes to the Olympics. 
 
 
 
 President Trump speaks during a Cabinet meeting at the White House on Dec. 20, 2017. (Jabin Botsford/The Washington Post) 
 
 [South Korea bets that talks with North could pay off] 
 
 In his Tuesday tweet, Trump wrote: "Sanctions and 'other' pressures are beginning to have a big impact on North Korea. Soldiers are dangerously fleeing to South Korea. Rocket man now wants to talk to South Korea for first time. Perhaps that is good news, perhaps not — we will see!" 
 
 Sanctions and “other” pressures are beginning to have a big impact on North Korea. Soldiers are dangerously fleeing to South Korea. Rocket man now wants to talk to South Korea for first time. Perhaps that is good news, perhaps not - we will see! — Donald J. Trump (@realDonaldTrump) January 2, 2018 
 
 Trump's North Korea comments came on a busy day of tweeting for the president, who called for the Justice Department to prosecute and perhaps jail Hillary Clinton adviser Huma Abedin and former FBI director James B. Comey; threatened to strip funding for the Palestinians; encouraged protesters in Iran; took credit for the safety record of commercial airlines; and attacked the news media. ||||| Media playback is unsupported on your device Media caption US ambassador Nikki Haley: "Kim Jong-un is begging for war" 
 
 The US envoy to the UN has urged the Security Council to take the "strongest possible measures" against North Korea after its latest nuclear test. 
 
 "The time has come to exhaust all diplomatic means before it is too late," Nikki Haley told an emergency meeting of the council in New York. 
 
 The US will circulate a draft resolution, for a vote next Monday. 
 
 South Korea is poised to scrap a warhead weight limit on its own missiles after talks with the US. 
 
 President Moon Jae-in reached agreement by phone with his counterpart, Donald Trump. Missiles are currently capped at 500kg (1,100lb). 
 
 The country carried out live-fire exercises on Monday, simulating an attack on the North's nuclear test site. 
 
 Reports suggest the North is preparing new test missile launches. It tested a nuclear bomb underground on Sunday. Estimates of its power range from 50 kilotonnes to 120 kilotonnes. A 50kt device would be about three times the size of the bomb that destroyed Hiroshima in 1945. 
 
 In other developments: 
 
 German Chancellor Angela Merkel said she would press for tougher EU sanctions on North Korea, agreeing with Mr Trump by phone on the need for stricter sanctions 
 
 Swiss President Doris Leuthard said her country was prepared to act as a mediator and called for more discreet negotiations, saying "Twitter won't be an adequate instrument" 
 
 Japan is planning, in the event of war, for a mass evacuation of nearly 60,000 Japanese citizens currently living in or visiting South Korea, Nikkei Asian Review reports 
 
 'Begging for war' 
 
 Opening Monday's meeting, UN Under Secretary General Jeffrey Feltman said North Korea's actions were destabilising global security, and he called on Pyongyang to abide by Security Council resolutions. 
 
 "The DPRK [North Korea] is the only country that continues to break the norm against nuclear test explosions," he said. 
 
 Image copyright AFP Image caption The UN Security Council last imposed sanctions in August, targeting North Korean exports 
 
 Ms Haley argued that only the strongest sanctions would enable the problem to be resolved through diplomacy. 
 
 North Korean leader Kim Jong-un had shown through his actions that he was "begging for war", she said. 
 
 "War is never something the United States wants," she continued. "We don't want it now but our country's patience is not unlimited." 
 
 She was speaking after President Trump warned the US might consider stopping all trade with any country doing business with North Korea. 
 
 "The United States will look at every country that does business with North Korea as a country that is giving aid to their reckless and dangerous nuclear intentions," Ms Haley said. 
 
 The British ambassador to the UN, Matthew Rycroft, said direct talks with North Korea were only possible if Pyongyang stopped the escalation. 
 
 "Dialogue will always be our end goal but returning to dialogue without a serious sign of intent from Pyongyang would be a set-up to failure," he said. "North Korea must change course to allow a return to dialogue." 
 
 China's envoy to the UN, Liu Jieyi, reiterated a call for all sides to return to negotiations. "The peninsula issue must be resolved peacefully," he said. "China will never allow chaos and war on the peninsula." 
 
 What happens next? 
 
 By Jonathan Marcus, BBC defence and diplomatic correspondent 
 
 China is key but it is a conflicted party. On the one hand it does not want to see a nuclear-armed North Korea and it has made its view clear to Pyongyang on many occasions. 
 
 However, it does not want to see the North Korean regime swept away. This would result in millions of refugees flooding into China and would probably result in a unified Korea very much in the US orbit. This is seen in Beijing as worse than having a difficult nuclear neighbour. 
 
 If China were to take the view that the coincidence of a rapidly advancing North Korean nuclear programme and the uncertainties of the Trump administration's diplomatic capabilities means that there is a very real risk of misunderstanding and catastrophe, then maybe it might bring much greater pressure to bear on Pyongyang. 
 
 North Korea is a very isolated country and China is both its major ally and economic prop. There is a lot more that China can do. North Korea's recent testing has been as much an embarrassment to China as it has angered the US. But the Chinese have a difficult diplomatic calculation to make. 
 
 Full version of analysis 
 
 What other sanctions remain? 
 
 Last month, the Security Council voted unanimously to ban North Korean exports and limit investments in the country. 
 
 Ms Haley did not spell out what additional measures might be taken but diplomats have suggested an oil embargo would have a crippling effect. 
 
 There could also be a ban on the North's national airline, curbs on North Koreans working abroad, and asset freezes and travel bans on officials. 
 
 How big was the latest test? 
 
 It was North Korea's sixth and most powerful nuclear test to date. The US Geological Survey recorded a resulting tremor at 6.3 magnitude. 
 
 Media playback is unsupported on your device Media caption Nuclear N Korea: What do we know? 
 
 Kim Jong-un was pictured on camera being shown what state media said was a new type of hydrogen bomb. 
 
 South Korea said it was now presumed that the North had reduced its nuclear warhead in size to below 500kg, and would be able to attach one to an intercontinental ballistic missile (ICBM). 
 
 But analysts have said the North's claims about miniaturisation should be treated with considerable caution. 
 
 Earlier on Monday, a South Korean defence ministry official said there were signs of "possibly more ballistic missile launches", including an ICBM. 
 
 How else are the South and its US ally responding? 
 
 Monday's drills simulated the targeting of the Punggye-ri nuclear site in Kilju County, where North Korea carried out its bomb test. Missiles were fired from the ground and rockets from fighter jets. 
 
 Media playback is unsupported on your device Media caption South Korea carries out live-fire drills in response to the nuclear test 
 
 The defence ministry in Seoul said there would be more live-fire drills in the South this month, involving Taurus air-to-surface missiles mounted on F-15 jets. 
 
 The ministry also told parliament the US would seek to deploy a nuclear-powered aircraft carrier to seas off the peninsula. 
 
 Four more launchers of the US Thaad (Terminal High-Altitude Area Defence) missile defence system -strongly opposed by China and Russia - would also be deployed to join two already at a site in Seongju, south of Seoul. 
 
 North Korea's nuclear tests ||||| Over the weekend, a former chairman of the joint chiefs of staff under two presidents said the U.S. is closer to nuclear war with North Korea "than we have ever been." | AP Photo CDC briefing to focus on preparing for nuclear war 
 
 The CDC wants the public to be prepared for nuclear war. 
 
 The agency has posted a notice touting a Jan. 16 briefing about the work that federal, state and local governments are doing in case of a possible nuclear strike. 
 
 Story Continued Below 
 
 “While a nuclear detonation is unlikely, it would have devastating results and there would be limited time to take critical protection steps,” the notice states. “Despite the fear surrounding such an event, planning and preparation can lessen deaths and illness.” 
 
 Presenters include Dan Sosin, CDC's deputy director and chief medical officer in the Office of Public Health Preparedness and Response, and experts on radiation safety and environmental hazards. 
 
 The briefing comes amid rising tensions between the United States and North Korea. President Donald Trump earlier this week fired off a taunting tweet in which he bragged that his nuclear arsenal is more powerful than North Korea’s. The CDC notice preceded that message. 
 
 “North Korean Leader Kim Jong Un just stated that the ‘Nuclear Button is on his desk at all times,’” Trump tweeted. “Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!” 
 
 POLITICO Pulse newsletter Get the latest on the health care fight, every weekday morning — in your inbox. Email Sign Up By signing up you agree to receive email newsletters or alerts from POLITICO. You can unsubscribe at any time. 
 
 Trump's tweets have alarmed policy experts who say they could exacerbate tensions. Over the weekend, Mike Mullen, former chairman of the Joint Chiefs of Staff under both former Presidents George W. Bush and Barack Obama, said the U.S. is closer to nuclear war with North Korea "than we have ever been." 
 
 CDC on Friday said that the event has been in the works since last April. 
 
 The briefing is part of the agency's monthly "Grand Rounds" sessions at its Atlanta headquarters. Upcoming briefings are mostly devoted to more conventional public health concerns, such as childhood vaccinations and hepatitis C.
– President Trump fired back at Kim Jong Un's claim to have a nuclear button on his desk by telling the North Korean leader that his button is bigger—and more functional. Kim "just stated that the 'Nuclear Button is on his desk at all times,'" Trump tweeted Tuesday. "Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!" Trump, who appears to be stepping up his rhetoric against Pyongyang after months of relatively restrained remarks, also brought back his "Rocket Man" nickname for Kim earlier Tuesday, the Washington Post reports. The reaction on social media ranged from shock that Trump was treating the prospect of nuclear war so blithely to delight that Trump was attacking Kim and upsetting "snowflakes" at the same time, the New York Times reports. Some—including CNN host Brian Stelter—argued that Trump might be having some kind of meltdown, or argued that Twitter should shut down his account for violating its terms of service. Others noted that Trump doesn't actually have a big nuclear button on his desk—to launch a nuclear strike, he would have to use a briefcase known as the "nuclear football." (Relations between North Korea and South Korea, meanwhile, may be improved by the Winter Olympics in the South next month.)