The United States expressed opposition Wednesday to any attempt to undermine Japan’s administration of a group of East China Sea islets, in reference to continued intrusions by Chinese government ships into Japanese waters around the islets despite repeated protests by Tokyo.

“We oppose any unilateral action that seeks to undermine Japan’s administration of the Senkaku Islands,” State Department spokeswoman Elizabeth Trudeau said at a press briefing.

Trudeau reaffirmed the U.S. position that although Washington does not take sides on the issue of sovereignty on the islands, they fall under the Japan-U.S. security treaty — meaning that the United States will defend Japan in the event of emergencies over the islets, which Beijing claims and calls Diaoyu.

“The Senkaku Islands have been under Japanese administration since the reversion of Okinawa in 1972. (As such) they fall within the scope of Article Five of the 1960 U.S.-Japan Treaty of Mutual Cooperation and Security,” she said.

As of Wednesday afternoon Japan time, seven Chinese government vessels and over 200 fishing vessels have been spotted operating in the contiguous zone just beyond Japanese waters around the islets, according to Japan Coast Guard officials.

“We are in close communication with the Japanese as allies and are also concerned about the increase of Chinese coast guard vessels in the vicinity of the islands,” Trudeau said.

China, which maintains the islands have been its inherent territory since ancient times, says it is a matter of course that Chinese vessels operate in waters near their country’s territory.