North Korea slams Japan's military buildup, vows counteraction

North Korea on Tuesday condemned Japan's planned military buildup outlined Tokyo's new security strategy, vowing to show with action how dangerous it is, state media said.

The remarks by a spokesperson of Pyongyang's foreign ministry came days after Japan unveiled its biggest military build-up since World War Two as regional tension with China and Russia's Ukraine invasion stoke war fears.

Japan's news security strategy effectively formalised a "new aggression policy" and would bring a fundamental change in East Asia's security environment, the spokesperson said.

The spokesperson slammed the United States for "exalting and instigating Japan's rearmament and re-invasion plan," saying Washington no right to raise issue with Pyongyang's efforts to bolster North Korea's defence.

"We will continue to demonstrate through practical actions how much we are concerned and displeased with Japan's unjust and greedy attempts to realise its ambitions," the spokesperson said in a statement carried by the official KCNA news agency.

In a separate statement, Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, said Pyongyang's efforts to develop a spy satellite were a "pressing priority directly linked to our security," and additional sanctions would not stop that.

South Korea would "cry out for some kind of international cooperation and try hard to impose additional sanctions on us," she said in the separate KCNA dispatch.

"But with our right to survival and development being threatened, why are we afraid of sanctions ... and why would we stop?"