Nine Taiwanese coast guard vessels entered Japanese waters Monday near disputed islands in the East China Sea to accompany a ship of protesters angry over the sinking nearby of a Taiwanese fishing boat, officials said.

Japan immediately denounced the incident as a violation of its territorial waters, amid a spike in tensions over the islands, known as Diaoyutai in Chinese and Senkaku in Japanese. Officials in Taiwan called it a mission to uphold its sovereignty over the disputed territory.

The vessels and the protest ship were in Japanese waters for about two and a half hours near the islands, defying repeated warnings from Japanese patrol boats, the Japanese coast guard said in a statement.

Taiwan’s Coast Guard Administration Vice Minister Cheng Chang-hsiung said the protesters got less than two-thirds of a mile (less than 1 kilometer) from an island in the chain, where they were blocked by nine Japanese patrol vessels. Cheng said Taiwan dispatched nine patrol vessels to protect the protesters’ ship along the way.

“We did not notify Japan of the operations beforehand because the operations aimed to maintain (Taiwan’s) sovereignty,” Cheng said in a televised news conference.

Japan contends the captain of a Taiwanese leisure fishing boat is responsible for last week’s collision with a Japanese coast guard vessel off the disputed islands. The Taiwanese captain claims the Japanese vessel rammed his craft. No one was injured in the incident. Taiwan recalled its envoy to Japan on Saturday in protest over the collision.

Japanese government spokesman Nobutaka Machimura denounced Taiwan’s violation of Japanese waters.

“The violation of territorial waters was extremely regrettable. The Senkaku islands are part of Japan, and this is beyond question,” Machimura said at a news conference.

Japan administers the islands, which are claimed by Taiwan as well as China. The value of the islands, about 1,260 miles (2,000 kilometers) southwest of Tokyo, has grown in recent years following the discovery of potentially rich gas reserves in the area.

Japanese public broadcaster NHK said it was unprecedented for a Taiwanese patrol vessel to enter Japanese waters. NHK said the protest ship carried around 40 activists, while the Japanese coast guard said about a dozen activists were spotted.

The small, uninhabited islands are located in rich fishing waters between the Japanese island of Okinawa and Taiwan.

The islands were seized by Japan in 1895 when it colonized Taiwan. The islets were then administered by the United States after World War II until control was turned over to Japan in 1972. But both Taiwan and China claim the islands have been theirs for centuries.

___

Associated Press correspondent Debby Wu in Taipei contributed to this report.