Japan has lodged a protest over China’s gas field developments in the East China Sea after confirming the building of new structures at Chinese facilities in the waters despite Tokyo’s repeated calls to refrain from such acts, Foreign Minister Fumio Kishida said Thursday.

“It is extremely regrettable that China is proceeding with unilateral developments in the East China Sea even though the boundary between Japan and China in the waters has not yet been fixed,” Kishida told reporters.

Deputy Chief Cabinet Secretary Koichi Hagiuda told a separate news conference that new structures and a flare had been confirmed this year at three of the 16 Chinese facilities near the median line between the two nations’ coastlines, in an indication that China continues to develop gas fields.

Japan has repeatedly protested against the moves, arguing that it went against a 2008 bilateral accord on joint gas development in the East China Sea.

Talks over the project have stalled, however, amid increasingly strained bilateral relations over territorial issues.

“Japan seeks to request China to implement the agreement as soon as possible,” Kishida said, noting that Japanese and Chinese leaders agreed in November last year to try and restart talks based on the agreement.