North Korea has declared itself no longer bound by the armistice that ended the Korean war more than half a century ago, and threatened to attack South Korea if it took part in US-led checks on vessels suspected of carrying weapons of mass destruction. The belligerent talk was accompanied by Pyongyang’s test-firing of two short-range missiles, bringing to five the number launched since its nuclear test on Monday. There were also reports that North Korea had begun operating its nuclear reprocessing plant at Yongbyon, which is capable of producing enough plutonium to make a bomb a year. Hillary Clinton, the US secretary of state, said Pyongyang would face “consequences” because of its moves, while South Korea responded to the sudden deterioration in mood by joining a US programme aimed at preventing the smuggling of nuclear, chemical or biological weapons. But a North Korean army spokesman warned its adversaries against forced maritime inspections, saying: “Any hostile act against our peaceful vessels, including search and seizure, will be considered an unpardonable infringement of our sovereignty and we will immediately respond with a powerful military strike.” North Korea also accused the US of “dragging” South Korea into the naval inspections programme as part…