"I have concerns over the lack of transparency in [China's] reinforcement of its national defense capability as well as the acceleration of maritime activities," Noda said during a parliamentary session.
"I expect China to play an appropriate role as a responsible member of the international community."
But at the same time, The Wall Street Journal reported, Yoda stressed the importance of trade relations between the two Asian economic powers, with China now Japan's largest export market. China has taken over as the world's second-largest economy behind the United States, while Japan has slipped to No. 3.
Noda, a former finance minister who took office two weeks ago, is known as a fiscal conservative, but his foreign policy stances are less clear, the newspaper said.
The two countries have become embroiled in disputes over China's maritime claims in the East China Sea, and Beijing has criticized Japan's wartime history.
In an apparent reference to China, Noda recently said: "Next year will be a period of change with a transition of leadership. They could stoke nationalistic sentiment and make provocations. We must be ready for any scenario."
China, for its part, took aim at Japan after Noda's election, when the state-run news agency Xinhua said, "It is vital to respect the feelings of the Asian people, including the Chinese, in dealing with Japan's history of aggression during the last century."
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