Believing China has begun extracting natural gas in a contested area of the East China Sea, Japan has lodged a protest with Beijing, the Japanese Foreign Ministry said Monday.
The Maritime Self-Defense Force has confirmed a flare at a structure thought to be a Chinese drilling rig, the ministry said.
The structure was put in position in May on the Chinese side of a Japan-proposed median line separating the two nations' exclusive economic zones in the sea, according to the ministry.
Tokyo has repeatedly called on Beijing to stop its development of gas fields near the median line while negotiations over a 2008 bilateral accord on joint gas development in the area remain stalled and to agree to resume the talks as soon as possible.
The negotiations were suspended in 2010 when bilateral tensions grew following a Chinese trawler's collision with a Japan Coast Guard vessel.
"It is extremely regrettable that the Chinese side is proceeding with unilateral development in the sea area, while the boundaries of (Japanese and Chinese) exclusive economic zones ... have yet to be fixed," the ministry said.
Takehiro Funakoshi, director general of the ministry's Asian and Oceanian Affairs Bureau, "strongly protested" to China over its latest activity through the Chinese Embassy in Tokyo, it said.
So far, Tokyo has found 18 structures set up by China on the Chinese side of the median line in the sea.