Tokyo has lodged protests to Beijing over the entry of Chinese coast guard ships into Japan’s territorial waters off disputed East China Sea islands and their refusal to move out for a third day Tuesday, Japanese officials said.

The two Chinese ships entered the Japanese-claimed waters Sunday morning, appearing to approach a Japanese fishing boat carrying three crew members. They have remained there, while ignoring repeated warnings and exit demands by the Japanese side, Japanese coast guard officials said.

Chinese coast guard vessels routinely violate territorial waters around the Japanese-controlled southern islands of Senkaku, which China calls Diaoyu and also claims.

Chief Cabinet Secretary Katsunobu Kato said Tuesday that it was “extremely regrettable” that the two Chinese coast guard ships were still in Japanese waters. Japan “strictly protested” to the Chinese side and demanded that the Chinese ships immediately move out of Japanese waters, Kato said.

He said Japan would firmly defend its territorial waters, land and airspace “with a sense of urgency.”

Japanese coast guard officials said the fishing boat with the three crew members was safely protected but declined to give any other details.

The Japanese government says Japan has had ownership of the islands since the late 1890s under international law. Tokyo also says Beijing started claiming its ownership around 1970 when possible undersea oil deposits near the islands were reported.

Japan sees China’s military development and increasingly assertive stance in the East and South China seas as a major security threat. Japan’s military invasion of China in the 1930s and 1940s remains a sore spot between the two sides.

Chinese foreign ministry spokesperson Zhao Lijian repeated China’s position. “The Diaoyu Islands and its affiliated islands are China’s inherent territory,” he said at a regular news conference in Beijing on Monday. “It is China’s inherent right to carry out law enforcement patrol in the waters of the Diaoyu Islands, and the Japanese side should respect this.”