Japan has lodged a protest with China over what it described as suspicious activity in a maritime area rich in gas deposits in the East China Sea, officials said Tuesday.
The two countries have a longstanding dispute over islands in the East China Sea controlled by Japan, which knows them as Senkaku, and claimed by China, which calls them Diaoyu.
Tokyo and Beijing agreed in June 2008 to cooperate over oil and gas resources in the area, but negotiations stopped two years later amid rising tensions and have not resumed.
The two countries have a longstanding dispute over islands in the East China Sea controlled by Japan, which knows them as Senkaku, and claimed by China, which calls them Diaoyu.
Tokyo and Beijing agreed in June 2008 to cooperate over oil and gas resources in the area, but negotiations stopped two years later amid rising tensions and have not resumed.