"The North Korean issues have made the regional security environment extremely difficult since the beginning of the 1990s," Koumura told an international security conference in this southern German city.

"The international community must continue to be united in demanding that North Korea provide 'a complete and correct declaration' of all its nuclear programmes, including nuclear weapons," and disable nuclear facilities, he said.

According to US intelligence, North Korea has produced enough plutonium for at least half a dozen nuclear weapons.

Koumura also called for improvements in North Korea's human rights situation, and for a settlement regarding the issue of Japanese citizens kidnapped by North Korea.

Japan, alongside China, the United States, Russia, Japan and the two Koreas, is currently engaged in the so-called six-party talks on the North Korean nuclear issue.

Koumura also expressed concern over China's military modernisation, saying it lacked transparency, notably as regards funding.

"Military modernisation and expansion of military expenses with a lack of transparency will result in increased regional concern," he said.

During his visit here Koumara met Saturday with Russian First Deputy Prime Minister Sergei Ivanov to discuss the issue of the Kuril islands, occupied by Russia since the end of World War II, a Japanese official said.

He also brought up the matter of an incursion early Saturday by a Russian Tupolev strategic bomber into Japanese airspace, the official added.

Japan scrambled two dozen jet fighters to intercept the long-range bomber and said it would lodge an official protest. Russia has denied that its bomber entered Japanese airspace.