Chinese People's Liberation Army navy sailors wait to attend a July 19 ceremony at the Great Hall of the People in Beijing. Japan raised concern Tuesday about China’s growing assertiveness in regional waters (Jason Lee/Reuters)

Japan voiced concern Tuesday about China’s growing assertiveness in regional waters at a time when it is becoming less clear who in Beijing is making decisions about the country’s military.

In its annual white paper, Japan’s Defense Ministry spoke of the “changing” influence of the Chinese military on foreign policy, although the document did not specifically say that the influence is growing. An increasingly “complex” relationship between the People’s Liberation Army and the ruling Communist Party presents a “risk management issue” for the region, Tokyo said.

Although Japan has long expressed unease about China’s lack of transparency on military spending and troop positioning, this was the first time its Defense Ministry had commented on the Chinese leadership’s actual decision-making process, Japanese officials said. Japan specifically noted the Communist Party’s once-a-decade leadership change, planned for later this year.

“There is a certain degree of wariness, not only in Japan but in the whole of East Asia, as to which direction China will be heading,” Defense Minister Satoshi Morimoto said at a news conference, according to the Kyodo News agency.

Tensions between the Asian neighbors have spiked in recent weeks amid the latest flare-up over a disputed, uninhabited island chain, which Japan recently said it would consider purchasing from a private landowner. The Defense Ministry paper called for Japan to beef up its presence in the disputed area with added surveillance.

As evidence of China’s alleged aggressiveness in western Pacific waters, particularly the East China Sea, the paper pointed to a “record number” of Chinese training exercises near Japanese islands, with at least one exercise involving an unmanned aerial vehicle. It also cited several instances in which Chinese helicopters flew close to Japanese destroyers. China has also increased its surveillance in the contested waters in recent years, the paper said, adding that the annual Chinese defense budget has more than doubled since 2007.

“China has been expanding and intensifying its activities in waters close to Japan,” the paper said. “These moves, together with the lack of transparency in its military and security affairs, are a matter of concern for the region and the international community, including Japan.”

The report drew a sharp response from Beijing, where a Defense Ministry spokesman called Japan’s remarks about the disputed islands “irresponsible.” An editorial in the nationalist China Daily on Tuesday took aim at Japan’s potential plan to buy the islands — known as Senkaku in Japan and Diaoyu in China — and said that Tokyo “seems to be devising a new but less cooperative strategy toward China.”

The Japanese Defense Ministry’s paper also touched on the security challenges posed by nuclear-armed North Korea and the importance of tightening cooperation with the United States.

For the eighth straight year, Tokyo reiterated its claim to another disputed group of islets controlled by South Korea. In response, Seoul summoned a Japanese diplomat and asked Japan to reconsider its claim.

“The Korean government strongly protests Japan’s re-inclusion of territorial claims to Dokdo,” Foreign Ministry spokesman Cho Tae-young said in a statement, referring to the isles by their Korean name. Cho said that Dokdo, known as Takeshima in Japan, was “clearly indigenous territory of Korea.”

Liu Liu, in Beijing, contributed to this report.