Seoul. The powerful sister of North Korean leader Kim Jong Un on Wednesday accused Japan of "transformation into a war state" as Tokyo beefs up its military stance in the Pacific.

Japan has been gradually moving away from its post-World War II pacifist status -- increasing military spending, ramping up defence pacts and deploying missile launchers to its outer islands.

Tokyo's defence minister said Tuesday the military needs to be boosted with a "sense of urgency and crisis", as a new government assessment warned of growing threats from China, Russia and North Korea.

In a statement carried by North Korean state media, Kim Yo Jong said Pyongyang's "leadership will set up additional military options which are obviously due to Japan's transformation".

"Japan, a war criminal state, is accelerating its transformation into a war state," said her statement published by the Korean Central News Agency.

Kim cited Tokyo's recent test-firing of Tomahawk long-range cruise missiles and its May participation in US-led drills in the Philippines as evidence of Washington's support for "dangerous military moves" in the Pacific.

Tokyo is moving "to formulate the possession of the capability for preemptive attack", she said. "We will never remain a passive onlooker to the military evolution of Japan which may pose a grave threat."

On Wednesday, Japan's defence ministry confirmed to AFP that the Tomahawk experiment last week was Japan's first.

Japan occupied all of Korea before its 1945 surrender in the Second World War, after which the peninsula was divided into separate states along the 38th parallel.

The legacy of the violent colonial period continues to weigh on the foreign policies of both North and South Korea.

"If the descendants of militarism, who have inherited the genes of cunning and aggression, have seized deadly weapons in their hands, something unpleasant will happen," Kim's statement said.

Japan has hosted US military bases ever since its surrender in World War II.

The nation raised its military expenditure by 9.7 percent to $62.2 billion in 2025 -- equivalent to 1.4 percent of GDP, its highest share since 1958.

China -- a key ally of North Korea -- has also recently expressed alarm at what it sees as "new militarism" by Japan.

Relations have worsened since Tokyo's hawkish new Prime Minister Sanae Takaichi made comments in November suggesting Chinese action to seize Taiwan could merit a reaction from Japan's military.

Beijing has long claimed Taiwan is part of its territory and has not ruled out taking it by force.

Pyongyang has repeatedly declared itself an "irreversible" nuclear state since leader Kim Jong Un's 2019 summit with US President Donald Trump collapsed over the scope of denuclearisation and sanctions relief.