North Korea has threatened to take unspecified stronger measures in response to recent international sanctions after it successfully launched a satellite into space in December.<br /><br />Pyongyang warns the action could exceed a promised nuclear test, which it had said would target its "enemy", the United States.<br /><br />The heightened rhetoric comes as a US scientist says North Korea could be close to a nuclear weapons breakthrough.<br /><br />Al Jazeera's Harry Fawcett reports from Seoul.
