North Korea is trying to develop a nuclear warhead that would fit on to a missile, South Korea's top military official has said. Gen Kim Tae-young told a parliamentary committee that the North was believed to have enough plutonium to make six or seven warheads. He said it was not clear if Pyongyang had succeeded in developing a warhead. North Korea recently back-tracked on an aid-for-disarmament deal, saying the US had not met its obligations. South Korean media have also reported that the North test-fired one or two short-range missiles into the sea off the west coast of the Korean peninsula on Tuesday. The North is also working on a long-range missile programme.