SEOUL, March 17 (UPI) -- North Korea on Monday vowed to "steadily update and strengthen" its nuclear arsenal, rejecting a joint statement by the Group of Seven Foreign Ministers calling for Pyongyang to give up its nuclear ambitions. The North's Foreign Ministry said its position as a nuclear weapons state has been "fixed permanently by the supreme law of its state." Advertisement "The DPRK's nuclear armed forces will exist forever as a powerful means of justice which defends the sovereignty of