From Daily Yomiuri On-Line: (Thanks to Professor Daniel Lynch for this link.)
The Senkaku Islands, a group of islands in the East China Sea, are Japanese territory. Therefore, the government had every right to put a private lighthouse built on Uotsurishima island, the largest of the Senkaku Islands, under state ownership.
To complement the action, the Japan Coast Guard will send personnel to conduct periodic maintenance checks on the facility, which was built by a domestic political organization.
These moves are aimed at showing neighboring countries that Japan has effective control over the Senkaku Islands. By doing so, the government is seeking to prevent a recurrence of an incident in which Japanese sovereignty was violated when a group of Chinese activists unlawfully landed on Uotsurishima in March 2004.