North Korea has lambasted South Korea for hosting a multi-national naval drill aimed at preventing the transfer of weapons of mass destruction calling it an open declaration of war. South Korea, for the first time, played a full part in the Proliferation Security Initiative on Thursday, with warships and aircraft from four countries staging an exercise off the southern port of Busan. Pyongyang's Korean Central News Agency termed the naval drill as a military provocation and an open declaration of war against North Korea. In a separate commentary the North's ruling communist party's official daily, Rodong Sinmun, said the country would build up its armed forces 1,000-fold, should the United States continue its military threat against Pyongyang. It warned that the provocative acts would bring nothing but military conflicts and worse inter-Korean relations.