Civilian and military police searched the homes and workplaces of Japanese navy officers and a destroyer yesterday in connection with leaked classified data on high-tech AEGIS radar systems, Defense Ministry officials said.
Yesterday's searches follow a series of investigations earlier this year into leaked intelligence on the missile defense system that Japan shares with the US.
The ministry officials declined to give details on the nature of the classified data, but said: "Information must not be leaked at the Defense Ministry and the Self-Defense Forces tasked with ensuring the safety of the nation."
The investigators searched the 4,650-tonne destroyer Shimakaze over the leaked secrets, Kyodo news agency said.
The leaked data, which included "special defense secrets," had been prepared for use in training courses for cadets who would be dealing with high-tech anti-air defence systems on AEGIS ships, Kyodo said.
Kyodo quoted investigators as saying that they suspected the navy officers had violated provisions protecting secrets related to the Japan-US mutual defense agreement.
Japanese police would not confirm the reports, saying only that investigations were under way.
``We want to find through these investigations as much as we can about what the exact situation is, while taking steps to prevent such a thing from happening again,'' newly appointed Defense Minister Masahiko Komura told reporters.
A scandal had erupted earlier this year when Japanese naval officers were found to have leaked classified information about the AEGIS radar system used on US and Japanese missile-defense capable ships. Japan has pledged to improve its handling of defense data.
US Secretary of Defense Robert Gates voiced his concerns when he met his Japanese counterpart Fumio Kyuma in Washington in late April, and Kyuma promised to take steps to prevent any recurrence of such leaks.
Earlier this month, Japan and the US sealed a deal which Japanese officials said would facilitate the exchange of classified information.
Public broadcaster NHK reported that investigators were also raiding the homes and offices of senior navy officials in the city of Yokosuka in Kanagawa Prefecture, near Tokyo.
Prefectural and navy investigators believe that computer disks containing classified data were illegally copied and circulated among dozens of students and instructors at a naval academy, the First Service School, in the western city of Etajima.
The case first surfaced in March, when police found one of the disks at the home of a Japanese naval officer in Kanagawa during a separate investigation into his Chinese wife's immigration status.
Japan deployed its first advanced US-developed Patriot missiles this year.