The Japanese government's comments about China's oil and gas development in the East China Sea were made to attract domestic support for new security bills, which face mounting opposition, according to observers.
The comments were made a day after Beijing warned that Tokyo's accusation leveled against legal development work by China in the East China Sea was deliberately creating antagonism.
On Wednesday, Japan released 14 photographs of Chinese offshore platforms on its Foreign Ministry website as "evidence" of China's "unilateral" gas field development near the "median line" between the Chinese and Japanese shores.
Kyodo News Agency said on Thursday that Japan's conservative forces, Japanese Prime Minister Shinzo Abe's political basis, have been increasingly unsatisfied with the improving atmosphere between Tokyo and Beijing.
The news agency quoted an unnamed diplomatic source as saying that the government expects to hype the perceived security threat from China to counteract strong domestic opposition.
Asked about the relationship between release of the photographs and the security bills on Wednesday, Japan's Chief Cabinet Secretary Yoshihide Suga said, "We made the decision after considering various factors."
Chinese Ambassador to Japan Cheng Yonghua said on Thursday that China has never admitted the "median line".
Chinese Foreign Ministry spokesman Lu Kang said on Wednesday that China's exploration of oil and gas in the East China Sea had been conducted in undisputed waters under China's jurisdiction and fully within its sovereignty.
He said Japan's actions were not constructive to the management and control of the situation or the improvement of bilateral ties.
Shen Shishun, a researcher of Japanese studies at the China Institute of International Studies, said Japan had long argued that China's exploitation on one side of the line could remove resources on the other side.
Wang Xiaopeng, an expert on maritime border issues at the Chinese Academy of Social Sciences, said Japanese "hype" over the issue is aimed at diverting international opposition to security drills and at increasing Japan's stake in future negotiations with China on the East China Sea issue.
