Japan has been vigilant against China's military buildup and North Korea's nuclear and missile threats amid what it considers a worsening security environment, an overview of the Defense Ministry's 2013 white paper said Tuesday.
The ministry says a lack of transparency in Chinese military and security affairs is "a concern" for the region and the international community, with the world's second-largest economy quadrupling its defense budget over the past decade.
The annual paper, a summary of which was presented to a meeting of the ruling Liberal Democratic Party, is expected to be approved by the Cabinet soon.
China has continued to send ships to waters near the Senkaku Islands since Japan nationalized them last year. The uninhibited islets are administered by Japan, but claimed by China.