North Korea escalates tensions Saturday announcing that it will shut down an industrial zone is operates jointly with the South.<br/> <br />The industrial zone is a vital source of hard currency for the impoverished state and hundreds of South Korean workers and vehicles enter daily after crossing the heavily armed border.<br/> <br />Many in the South saw the North's willingness to keep the zone open as a sign Pyongyang will not risk losing a lucrative source of foreign currency by mounting a real act of aggression.<br/> <br />The threat to shut it down could sharply escalate tensions because it would suspend a symbolic joint project run by the rivals.<br/> <br />The North has previously suspended operations at the factory zone at the height of political tensions with the South, only to let it resume operations later.<br/> <br />Earlier the North said it was entering a "state of war" with South Korea.<br/> <br />The two Koreas have been technically in a state of war for six decades under a truce that ended their co
