North Korea's nuclear test: Fallout THE nuclear explosion that North Korea set off on February 12th deep in a hillside in the country's north-east would, the regime immediately assured, pose no "negative impact on the surrounding ecological environment." The negative impact on North-East Asia's security environment, on the other hand, was instant. The nuclear test came in defiance even of China, North Korea's supposed ally. It took place just hours before Barack Obama gave his state-of-the-union address at the start of his second term as president. It was, North Korea insisted, a "self-defensive measure" against "continued hostility" by America. "Even stronger" measures were threatened. North Koreans, at least in front of the cameras, appeared jubilant. It will take a while to know what exactly went on at the Punggye-ri test site. The official news agency, KCNA, said the bomb was smaller, lighter and more powerful than the previous two tested in October 2006 and May 2009. Whether that is true or not, the regime's goal is surely to make a warhead compact enough to sit atop its Unha-3 rocket, one of which put a satellite into space in December. With the right re-entry and weapons-guiding technologies, North Korea would then have an intercontinental ballistic missile with the ability to strike America. South Korea's defence ministry says the seismic impact of the blast indicated a power equivalent to 6-7 kilotons of TNT, compared with 2-6 kilotons in 2009. KCNA avoided mention of what fissile material was used - plutonium (as in the previous tests) or highly enriched uranium. If uranium, it would make the North's nuclear programme more threatening. The country has plentiful deposits of uranium ore, whereas its supply of plutonium is limited. The uranium enrichment process is also easy to conceal, devices can be made more quickly, and the risk of proliferation with nuclear allies such as Iran is higher. Condemnation of the blast was swift. The United Nations Security Council, which had warned North Korea against conducting a test, threatened further action. Diplomats expect existing UN sanctions to be strengthened. Yet the best way to put real pressure on the regime would be to hit it financially, freezing the accounts to which regime members have access. In his address, Mr Obama promised action. He said America would stand by its allies in the region and strengthen its missile defences. Yet the means for disciplining North Korea are limited. For a start, no matter how isolated the regime, Kim Jong Un, the young dictator, in the job for just over a year, seems to have inherited from his father and grandfather the conviction that a nuclear capability is a non-negotiable survival strategy. That makes the goal of denuclearisation, a premise for any renewed American engagement with North Korea, seem a pipe dream, at least for as long as the regime survives. If North Korea sets any store by the stalled six-party talks convened by China and including Russia, South Korea, Japan and America, it will be as a forum not for bargaining away its capability but for acknowledging the North as a nuclear power. The North Korean challenge comes at a time when relationships among North-East Asian neighbours are unsettled. In addition, the neighbours have internal differences over how to deal with North Korea. Take China, where some want more toughness than the government has so far shown against North Korea - something that would go down well with America and its allies, too. Many Chinese are furious that, by ignoring urgings not to conduct a test, North Korea has poked big brother in the eye. China swiftly backed the UN rebuke, and its foreign minister summoned North Korea's ambassador in Beijing for a dressing-down. The timing of the test cannot have helped, coinciding with China's lunar-new-year festivities. Some Chinese bloggers are splenetic. All the same, Xi Jinping, who took over as Communist Party chief in November, is unlikely to change China's policy towards the North by cutting off border trade (see article) or energy supplies. Nor will he constrict the regime's access to cash. That might risk precipitating collapse, or goading the Pyongyang leadership into starting a war on the Korean peninsula. Divisions may widen inside South Korea, too. The president-elect, Park Geun-hye, takes office on February 25th. Though of the same conservative party as the outgoing leader, Lee Myung-bak (loathed by the Kim regime for his hard line), Ms Park had promised a more "trust-based" relationship. Many voters will still hope she is more conciliatory towards the North. But she warned after the test that the North's pursuit of nuclear weapons would bring it "self-destruction." And on February 14th the South unveiled a new cruise missile that it said could "strike the window of the office of North Korea's leadership." Regional tensions will make a unified response more difficult. Relations between China and Japan have sunk to a nadir in a dispute over islands in the East China Sea. Michael Green of the Centre for Strategic and International Studies in Washington, DC, says America could encourage more trilateral co-operation with its two closest allies, Japan and South Korea, including on missile defence. But this would rankle China, where many think the American aim is to "contain" them. Meanwhile, relations between Japan and South Korea are also troubled by disputed rocks, though less dangerously than in the Sino-Japanese case. Japan, under its new prime minister, Shinzo Abe, is putting forward ideas that might please America but irk China and South Korea. Mr Abe, who will meet Mr Obama in Washington next week, is keen to reinterpret Japan's constitution, in which the country renounces war, in ways that give Japan the right to engage in collective self-defence in the face of security threats. He wants Japan to be able to help an ally when it is in trouble - by, for instance, shooting down North Korean missiles that are heading for the United States. American policymakers have generally favoured such a shift. However, some Chinese and South Koreans view Mr Abe as a hawk with revisionist views about Japan's past imperialist brutalities. So some members of the Obama administration are nervous that Mr Abe's ambitions may increase regional tensions. Mr Green believes such fears to be overblown. In its essence, he says, collective self-defence is not a threatening aspiration. Uncertainty also comes with John Kerry's replacement of Hillary Clinton as America's secretary of state. Mrs Clinton was robust in the face of Chinese assertiveness over claims in the East and South China Seas. Mr Kerry may prove milder. But with a nuclear-charged North Korea, and China's and Japan's relations so bad, the neighbours urgently need to get to know each other better.