Japan's 2018 defence white paper also took aim at China's rise as a military power, saying Beijing was sparking "strong security concerns in the region and international community, including Japan".

Last year's defence review was published at the height of the tensions with North Korea, amid nuclear and missile tests and with US President Donald Trump threatening to rain down "fire and fury" on Pyongyang if it kept up its threats.

But since then, a spectacular diplomatic detente has taken place, culminating in the historic summit between Trump and the North's leader Kim Jong Un in Singapore on June 12.

Nevertheless, Tokyo insisted on Tuesday: "There is no change in our basic recognition concerning the threat of North Korea's nuclear weapons and missiles."

Pyongyang continues to post "an unprecedentedly serious and imminent threat to Japan's security and (to) significantly damage the peace and security of the region and the international community", according to Tokyo.

Japanese Defence Minister Itsunori Onodera acknowledged in the document that North Korea had begun dialogue with former foes the US and South Korea.

"But we cannot overlook the fact that, even to this day, it possesses and fully deploys several hundred missiles that put nearly all of Japan within range," stressed the minister.

In response, Japan is steadily upgrading its capacity to shield the nation from the North's arsenal, including a plan to spend some $4.2 billion over the next three decades on installing and operating US radar systems.

The defence ministry is expected later this week to request a record 5.3 trillion yen ($47.6 billion) for the budget for the fiscal year starting from April.

Despite the historic handshake in Singapore, there has been little progress in denuclearising the Korean peninsula and Washington-Pyongyang relations appear to have taken a turn for the worse, with Trump abruptly scrapping a planned visit to the North by Secretary of State Mike Pompeo.

The white paper also reiterated Japan's worries about China's increasing military spending and expanding naval ambitions.

It complained that Beijing was trying to "change the status quo by coercion", referring to such actions as building up disputed islands in the South China Sea and expanding naval activities around East China Sea islands disputed with Japan.

The white paper drew ire from Seoul by repeating Tokyo's longstanding claim of sovereignty over islands which Japan calls Takeshima.

The islands are controlled by South Korea, which calls them Dokdo.

"The Japanese government must bear in mind that repeating such unjustifiable and groundless allegations over Dokdo will not be helpful at all in building forward-looking relations between the two countries," the South Korean foreign ministry said in a statement.