Four Chinese government ships sailed into the territorial waters of disputed islands controlled by Tokyo in the East China Sea on Friday, Japan’s coastguard said. The maritime surveillance vessels entered the 12-nautical-mile zone around Kubashima, one of the islands in the chain called the Senkakus by Japan and the Diaoyus by China, shortly before 1pm. Chinese vessels have been spotted in and around the territorial waters almost every day for the last two months. Beijing on Monday branded a US-Japan security treaty “a product of the cold war” when Washington lawmakers reiterated their support for Japan by passing amendment to the National Defence Authorisation Bill. The amendment 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”. 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, prompting the Japanese government to nationalise them.