A US-Japanese plan to deal with a possible military conflict across the Taiwan Straits has caused "grave concern" in Beijing.

Washington and Tokyo will discuss a contingency plan in case of a "crisis" situation arising in areas around Japan, including the Taiwan Straits, Kyodo News Agency reported yesterday.

The report quoted several sources familiar with Japan-US military cooperation as saying the two sides have reached consensus on the necessity for such a contingency plan and will soon begin discussing the details.

Responding to the reports, Foreign Ministry spokesman Liu Jianchao told a news conference yesterday: "Taiwan is an inseparable part of China's territory and any arrangement between Japan and the United States should respect and abide by the one-China principle."

"We have expressed grave concern," he added, calling secessionist forces in Taiwan "the greatest threat to peace and stability across the Taiwan Straits".

He said both Sino-Japanese and Sino-US relations are developing smoothly, and expressed the hope that the two countries will take more active measures conducive to the healthy development of their relationship with China.

However, Chinese experts on international studies warn that the strengthening of the US-Japanese alliance is targeted at China and would further complicate the nation's security environment.

Tao Wenzhao, a senior researcher with the Chinese Academy of Social Sciences, noted that the alliance aims to act as "a policeman" in the Taiwan Straits and play a dominant role in the region.

Wu Xinbo, a professor with the Center of America Studies at Fudan University, pointed out in a published article that enhanced security ties between Washington and Tokyo since the mid-1990s have reshaped the East Asian security environment; and Japan has showed increased assertiveness and willingness to work militarily with the United States.

He said interaction between Washington and Tokyo on the Taiwan issue has been increasing, with Tokyo more actively consulting and coordinating with Washington in its "relations" with the island province from listing Taiwan as a common strategic objective to working on a joint war plan for the Taiwan Straits.

Japanese Prime Minister Shinzo Abe, without referring to the "Taiwan contingency plan", said yesterday that his country would pursue assertive foreign policies and strengthen its ties with the United States and Europe in response to new security threats in the region.