China on Thursday lambasted the leaders of the United States and Japan for having confirmed that their bilateral security treaty covers the disputed Senkaku Islands, arguing they are "China's inherent territory."

Chinese Foreign Ministry spokesman Zhao Lijian also told reporters, "The U.S.-Japan Security Treaty is a product of the Cold War. It should not harm the interests of third parties and endanger regional peace and stability."

File photo taken in September 2012 shows the Japan-controlled Senkaku Islands in the East China Sea. Taiwan and China claim the uninhabited islands as their own. (Kyodo)

The group of uninhabited islets in the East China Sea, called Diaoyu in China, are controlled by Tokyo but claimed by Beijing. Sino-Japanese ties have been often frayed by the territorial issue.

Zhao's remarks came after new U.S. President Joe Biden was quoted by the White House as telling Japanese Prime Minister Yoshihide Suga that the United States has an "unwavering commitment" to defending Japan under the treaty, "which includes" the Senkakus.

Late last week, meanwhile, China passed a bill that allows its coast guard to use weapons when foreign ships involved in illegal activities in waters claimed by Beijing fail to obey orders, in a move that would complicate relations with its neighbor Japan.

Fears are mounting that the legislation could target Japanese vessels navigating around the Senkakus.

During their first phone talks since Biden took office on Jan. 20, the two leaders also "discussed the U.S.-Japan alliance and affirmed its importance as the cornerstone of peace and prosperity in a free and open Indo-Pacific," the White House said.

The vision of a "free and open Indo-Pacific" has been initiated by the United States and Japan, apparently aimed at countering China's rising assertiveness in the nearby waters as well as its growing economic influence in the region and across the globe.

"Exchanges between relevant countries should be conducive to mutual trust among nations in the region and to regional peace, stability and prosperity," Zhao said, without directly criticizing the United States and Japan.

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