China's increasingly assertive diplomatic and security postures present a much tougher challenge than its economic rise, requiring closer cooperation between the United States and its allies such as Japan to manage the situation, scholars from American think tanks said at a recent symposium in Tokyo.

Meanwhile, recent upheavals that have swept countries in the Middle East and North Africa make it more difficult for the U.S. to seek political stability in the region to protect its key interests there, including energy security that is also vital to Japan, they said.

The experts from U.S. think tanks were speaking at the Jan. 28 symposium organized by the Keizai Koho Center under the theme "Japan's security, economic situation and foreign affairs." Tsuneo Watanabe, director and senior fellow of the Tokyo Foundation, served as moderator of discussions.