China has expressed serious concern and firm opposition to a U.S. bill that regards China's territory as under the authority of a U.S.-Japan security pact.

Chinese Foreign Ministry spokesman Hong Lei speaks at a regular press briefing on Dec. 3, 2012.

At a regular press briefing, Chinese Foreign Ministry spokesman Hong Lei told reporters, "The Chinese side expresses serious concern and firm opposition to the U.S. Senate's amendment to the National Defense Authorization Act which involves the Diaoyu Island and its affiliated islets."

In the bill, which the U.S. Senate passed last week, the United States reaffirmed that it "takes no position" on the ultimate sovereignty of the Diaoyu Islands. However, the bill notes that Japan has the rights of administration over the territory and that "unilateral actions of a third party" would not affect its position.

Hong said the Diaoyu Island and its affiliated islets have always been the inherent territory of China since ancient times, and China has undisputed sovereignty over the Diaoyu Islands.

According to the U.S. bill, any armed attack "in the territories under the administration of Japan" would be met under the Treaty of Mutual Cooperation and Security.

Hong called the Treaty of Mutual Cooperation and Security between the United States and Japan as a "product of the Cold War era", saying it should not go beyond bilateral scopes, nor undermine the interests of a third party.

Hong said the U.S. side has repeatedly stated that it will not take sides on territory disputes between China and Japan.

He said the U.S. side "should not send out signals that conflict with each other." He expressed the hope that the U.S. side would "proceed from the general situation of peace and stability of the region", "keep its words" and "do more things that are conducive to peace and stability in the region."