A Chinese government ship briefly sailed into the territorial waters of disputed islands controlled by Tokyo in the East China Sea on Tuesday, Japan's coastguard said.

The maritime surveillance vessel entered the 12-nautical-mile zone around Minamikojima, one of the islands in the chain called the Senkakus by Japan and the Diaoyus by China, shortly after noon (0300 GMT) for about 10 minutes.

Chinese vessels have been spotted in and around the territorial waters almost every day for the last two months.

The latest episode came a day after Beijing branded a US-Japan security treaty "a product of the Cold War" when Washington lawmakers bolstered Japan in its territorial dispute with China over the islands.

The amendment, attached to the National Defense Authorization Bill, noted that while the United States "takes no position" on the ultimate sovereignty of the territory, it "acknowledges the administration of Japan over the Senkaku Islands".

It added that "unilateral actions of a third party" would not affect its position.

The legislation passed last week reaffirmed the US commitment to Japan under the Treaty of Mutual Cooperation and Security and warned that an armed attack against either party "in the territories under the administration of Japan" could be met with force.

The sovereignty of the islands has been a source of friction for decades, but the row erupted earlier this year after the nationalist governor of Tokyo said he wanted to buy them for the city, forcing the Japanese government to nationalise them.