North Korea Warns Japan Over Its 'Very Dangerous' Military Buildup

North Korea on Tuesday condemned a Japanese military buildup outlined in a new security strategy, warning that Japan would soon see the consequences of its dangerous decision, while also hinting at a technical advance in its long-range missile system.

Japan last week announced its biggest military build-up since World War Two as tension with China and a hostile North Korea and Russia's Ukraine invasion stoke fears of war.

North Korea's foreign ministry said Japan had effectively formalised "the capability for preemptive attack" with its new strategy that would bring a fundamental change to East Asia's security environment.

"The DPRK makes it clear once again that it has the right to take a resolute and decisive military step to defend its national sovereignty, territorial integrity and fundamental interests in the light of the complexity of the regional security environment caused by Japan's action," the official said in a statement carried by the North's KCNA news agency.

The spokesman referred to North Korea by the initials of its official name, the Democratic People's Republic of Korea.

Japan would realise "it made a wrong and very dangerous" decision, the spokesperson said, referring to a "shuddering shiver to be felt soon".

North Korea has tested an unprecedented number of missiles this year, including an ICBM designed to reach the U.S. mainland, in defiance of international sanctions.

Several of the North Korean missiles have flown over Japan, or landed in waters near it, drawing condemnation from the staunch U.S. ally.

The North Korean spokesperson also criticised the United States for "conniving and instigating Japan's rearmament and reinvasion scheme" saying the United States had no right to question North Korea's defences.

In a separate statement, Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, hinted at a technological advance in its ICBM system, and denounced questions over what North Korea said was its bid to develop a spy satellite.

North Korea fired two medium-range ballistic missiles off its east coast on Sunday in what it called an "important" test for the development of a reconnaissance satellite that it hopes to complete by April.

Experts have raised doubts over the level of North Korea's satellite technology but Kim Yo Jong derided the questions and suggested that North Korea's technical abilities included new ICBM developments.

North Korea has test-fired its ICBMs at a steep angle and analysts say a normal launch angle requires more sophisticated technology to resist heat generated during re-entry into the atmosphere.

"I can clear up their doubt about it," Kim Yo Jong said. "They will immediately recognise it in case we launch an ICBM in the way of a real angle firing straight off."

Kim Yo Jong dismissed any threat of new sanctions.

"At this time when our right to existence and development is being threatened, how can we stop our advance for fear of sanctions that we have experienced abominably, not for the first time," she said.