Japan’s Defense Ministry rolled out its defense white paper Tuesday, outlining various threats to the country and the Asia Pacific region. The paper gave particular attention to China, citing the Asian military giant’s maritime ambitions as one of the biggest concerns.

“Coupled with a lack of transparency in terms of military and security affairs, China’s military development is of concern to the regional international community, including our country,” Defense Minister Gen. Nakatani said in news conference, according to the Japan Times. “Our country needs to observe it closely.”

Though Japan took issue with several areas China was operating in, including the South China Sea, the most urgent concern was with an offshore gas platform that China has been constructing in the disputed waters of the East China Sea since June 2013. Plans of gas drilling in the East China Sea were initially mutually agreed upon by both parties in 2008. However, because the two sides have not been able to agree on a maritime boundary between their two exclusive economic zones, Japan expressed wishes to postpone the gas field project until a mutually agreed upon demarcation was met. Under Japan’s proposed demarcations, China’s gas platform was still theoretically on the Chinese side, the Japan Times reported. Still, Japan worried that the close proximity to Japan’s exclusive economic zone, about 16 miles west from the median line, meant China’s gas project could be siphoning gas from Japan-claimed seabeds.

“Our country has repeatedly lodged protests with China’s unilateral development and urged it to stop the construction work,” the defense paper said.

The paper also specifically noted concern over military activity in the East China Sea. “Activities by Chinese naval and air force aircraft, which apparently gather information about our country, have been observed frequently,” the paper said, adding that a Japanese “self-defense” fighter jet made a record 464 flights last year in response to Chinese aircrafts that neared Japanese airspace.