South Korean and US officials fear North Korea could be preparing to detonate a nuclear bomb for the third time to coincide with the imminent launch of a long-range rocket. North Korea has already moved a rocket to a launch-pad in the north-west of the country, arguing it is going to put a satellite into orbit around April 15, to celebrate the centenary of the birth of Kim Il-sung, founder of the nation. It plans to launch it between April 12 and 16. South Korea, Japan and the US have condemned the launch, arguing North Korea is advancing military ballistics under the smokescreen of building a satellite programme. While a new nuclear test would spark outrage, the international community has almost no room to add to the extensive sanctions already imposed against Pyongyang because of its pursuit of atomic weapons and intercontinental ballistics. An unnamed official at South Korea's intelligence service told the Yonhap state news agency that North Korea was digging a tunnel close to the Chinese border in an area where it tested nuclear bombs in 2006 and 2009. South Korea's state broadcaster KBS showed satellite images of mounds of supposedly freshly excavated dirt piled around the mouth of a shaft at Punggye-ri in Hamkyong province, scene of previous nuclear tests. It did not identify the source of the images, but it is common for Seoul's spy agency to issue information through state-owned media. Separately, a defence official said it was possible that North Korea was following the same cycle as 2009 when it followed a long-range rocket launch with a nuclear test. Such a test this year could be a show of force from Kim Jong-eun, the new leader, as he may be close to weaponising a warhead to fit on a long-range nuclear missile. Siegfried Hecker, a US atomic scientist who has visited North Korea's atomic facilities, argues Pyongyang needs one more test to be able to weaponise its fissile material. Still, security officials have noted that Pyongyang may not be keen to conduct a third test for fear of depleting its stocks of fissile material, which are estimated to be enough to build only a handful of primitive warheads. Pyongyang's launch has also scuppered a food deal with the US. Washington had been planning to send 240,000 tonnes of food to starving North Koreans on the condition that North Korea suspend atomic tests, missile launches and uranium enrichment.