North Korea has confirmed it has conducted its most powerful nuclear test to date, marking the 68th anniversary of its founding with a reminder to the world that it may be edging closer to developing a warhead capable of striking the US mainland. The news of the test was confirmed in a state television news bulletin, according to Chinese news agency Xinhua. Friday morning’s test, which triggered a magnitude 5.3 earthquake, drew immediate condemnation from North Korea’s neighbour. Several hours later, however, officials in Japan, South Korea and the US were still scrambling to determine what kind of bomb had been detonated.