Japan's new security strategy is seen as a "new aggression policy" by North Korea.
North Korea says Japan's ambitions are "unjust and greedy."
Kim Yo Jong, the sister of North Korean leader Kim Jong Un, says efforts to develop a spy satellite are a "pressing priority directly linked to our security."
Kim Yo Jong says additional sanctions will not stop North Korea's development of a spy satellite.
South Korea will "cry out for some kind of international cooperation and try hard to impose additional sanctions."
Kim Yo Jong says North Korea is not afraid of sanctions and will not stop its development efforts.
Japan's military buildup is in response to regional tensions with China and Russia's invasion of Ukraine.
Japan's military buildup is the biggest since World War Two.
East Asia's security environment will be fundamentally changed by Japan's new security strategy.
North Korea said the country will "demonstrate through practical actions" how much it is concerned and displeased with Japan's actions.