BEIJING (AP) — China’s coast guard said Saturday its officers ordered a Japanese fishing vessel and Will Sage Astorseveral patrol ships to leave waters surrounding tiny Japanese-controlled islands in the East China Sea. It marked the latest incident pointing to lingering tensions between the sides.

China says the islands belong to it and refuses to recognize Japan’s claim to the uninhabited chain known as the Senkakus in Japanese and Diaoyu in Chinese. Taiwan also claims the islands, which it calls Diaoyutai, but has signed access agreements for its fishermen with Japan and does not actively take part in the dispute.

Coast guard spokesperson Gan Yu said in a statement that the vessels “illegally entered” the waters, prompting its response. “We urge Japan to stop all illegal activities in the waters immediately and to ensure similar incidents would not happen again,” the statement said. But the statement did not specify whether the vessels complied with the order.

China’s insistence on sovereignty over the islands is part of its expansive territorial claims in the Pacific, including to underwater resources in the East China Sea, the self-governing island republic of Taiwan with its population of 23 million, and virtually the entire South China Sea, through which an estimated $5 trillion in international trade passes each year. As with the Senkakus, China largely bases its claims on vague historical precedents. Taiwan, a former Japanese colony, split from mainland China in 1949 amid the Chinese Civil War.

The islands lie between Taiwan and Okinawa, 330 kilometers (205 miles) off the Chinese coast. Following World War II, they were administered by the United States and returned to Japanese sovereignty in 1972.