Japan protests over China warship off disputed islands

Japan criticized Beijing for escalating tensions in the East China Sea on Thursday, after a Chinese warship was spotted near disputed islands for the first time.

Japan said a Chinese navy frigate was seen off the coast of the Japanese-controlled Senkaku islands, also claimed by China and called the Diaoyu islands. The ship did not violate Japan’s territorial waters. Chinese coast guard vessels routinely patrol the area.

Yoshihide Suga, Japan's chief cabinet secretary, said his country was “extremely concerned about the action that unilaterally escalates tension in the area.”

Tokyo summoned China's ambassador over the incident to "express a serious concern."

China's defense ministry said it was looking into the matter but that it had a right to sail in Chinese waters, according to Reuters.

Japan said it was also investigating the presence of three Russian warships in the area around the same time.