North Korea said it will prepare its nuclear force for an all-out war against the United States as it blames Washington for the escalating tensions on the Korean Peninsula.The President of the Supreme People's Assembly, Kim Yong-nam said that Pyongyang would expand the quantity and quality of its nuclear force which is the "treasure of a unified Korea", press tv reported.He made the comments during a memorial event, which was held in the capital, Pyongyang, on Sunday on the eve of the 101st anniversary of the birthday of late leader Kim Il-sung.The official added that Pyongyang's "invincible defense forces" that are armed with strengthening "nuclear deterrence forces" would "unfold a total fight against the US, acting in accordance with a wartime scenario".The remarks followed Pyongyang's rejection of South Korea's proposal to resolve tensions through dialogue as the North said the offer was "a cunning ploy to hide the South's policy of confrontation"Meanwhile, US Secretary of State who arrived in Japan on the last day of his four-day visit to Asia to discuss recent tensions on the Korean peninsula earlier on Sunday, has said that Washington is "fully committed to the defense of Japan."In Friday, the Japanese Daily Press reported that Pyongyang had issued a warning to Tokyo to stop its "hostile posture" against North Korea or else Tokyo would be the main target in case of a war in the region.Tensions sharply heightened after the US dispatched nuclear-capable B-52s and B-2 stealth bombers to participate in joint military drills with South Korea.The moves prompted Pyongyang to step up its war rhetoric, authorizing its army to launch preemptive nuclear strikes on the US.North Korea has also said its military should be prepared to attack "all US military bases in the Asia-Pacific region, including the US mainland, Hawaii, and Guam," in addition to South Korea.