Japan, which lies across the sea from North Korea, has been wary for decades over its missile development.
Japan, which lies across the sea from North Korea, has been wary for decades over its missile development as well as Pyongyang's history of abducting Japanese citizens to train its spies.
North Korea has increasingly been firing missiles into the waters between the two countries and last month launched two intercontinental ballistic missiles (ICMBs), with leader Kim Jong-Un boasting the entire United States was within reach.
While experts and officals doubt the North's missile technology is really that advanced, the country has made steady progress in recent years under Kim.
"Especially since last year, when it pushed ahead with two nuclear tests and launched more than 20 ballistic missiles, it has posed a new level of threat," Defence Minister Itsunori Onodera said in the white paper.
Onodera, reappointed to the post last week after having served in the position 2012-2014, also reiterated phrasing from past reports calling the danger from North Korea "significant and imminent".
"It is conceivable that, over time, the risk will increase for the deployment of ballistic missiles with nuclear warheads that put our nation within their reach," the Japanese-language paper said.
The UN Security Council at the weekend unanimously approved tough new sanctions against North Korea that could cost Pyongyang $1 billion a year.
Japan's white paper also reiterated Tokyo's concerns about China's efforts to expand its military influence and territorial claims, particularly in waters around Japan.
The government has long complained about Beijing's routine dispatch of coastguard ships to Japan's territorial waters surrounding disputed islands in East China Sea.
Tokyo controls the islands as the Senkaku while Beijing claims them as the Diaoyu.
Coastguards from the two sides have engaged in maritime standoffs, while their militaries have also had close calls. Experts fear such situations may lead to unplanned clashes.
"Regarding China, we are strongly concerned about its impact on the regional and global security environment as it continues to make unilateral, uncompromising assertions that are incompatible with the existing international order," Onodera said.