The conservative Sankei Shimbun said the government commissioned a report by experts completed in September on the possibility of creating indigenous nuclear warheads.

The study found that Japan needed three to five years, investment of 200 to 300 billion yen (1.7 to 2.5 billion dollars) and hundreds of engineers just for the prototype of a small-scale nuclear warhead.

"Even if Japan says hypothetically it can defend itself with nuclear arms, it could not deter the North Korean nuclear threat immediately and independently," the newspaper wrote, summarizing the report.

Even though Japan has plants for uranium enrichment and the technology for reprocessing, technological constraints would prevent converting the facilities to develop nuclear weapons, it said.

"Japan would have to address technological issues that are not yet familiar to the nation to create small nuclear warheads," the daily wrote.

Officials denied the reported study.

"The government is absolutely unaware of it," said Chief Cabinet Secretary Yasuhisa Shiozaki, the government spokesman.

Japan, the only nation to have been attacked with nuclear bombs, bans the production, possession or presence of atomic weapons on its soil.

Prime Minister Shinzo Abe has said his government will not change its stance, but two of his top aides have repeatedly called for Japan at least to debate going nuclear.

One of them, Foreign Minister Taro Aso, said last month that Japan could already produce nuclear weapons if it chose to, due to its high level of technology and civilian nuclear industry.

Japan, which is almost entirely dependent on foreign oil and gas, relies on nuclear production for one-third of its energy requirements.

earlier related report
US asks to install anti-missile radar in Japan: report
Tokyo (AFP) Dec 26 - The United States has asked to install anti-ballistic missile radars in Japan, following North Korea's nuclear weapons test in October and missile launches in July, a report said Tuesday. US military troops and the US Department of Defense have lodged a request with Japan's Defense Agency to locate a radar in Japan aimed at counter-attacking inter-continental ballistic missiles, the Asahi Shimbun newspaper reported, without clarifying sources.

Japan's Defense Agency, following the US approach, is considering the plan, in light of Japan-US Security Treaty, which demands "providing security of Japan and keeping peace in the Far East" as conditions for offering US troops facilities in Japan, the report said.

Japan was prompted to boost its missile defenses in cooperation with the United States in 1998 when North Korea sent a suspected long-range missile over its main island and into the Pacific.

North Korea's October 9 atom bomb test, in addition to its July 5 firing of seven missiles into the Sea of Japan (East Sea), also fueled the drive for the joint missile scheme.

Japan's post-World War II pacifist constitution bans waging war as means of resolving international conflicts, and providing support to foreign troops except for the purpose of Japan's self-defense is politically controversial.

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