TOKYO (AP) -- Japan's foreign minister summoned China's ambassador Tuesday and lodged a protest over the increased number of Chinese vessels in waters near disputed islands in the East China Sea.
The move by Fumio Kishida comes as the number of Chinese coast guard ships around the islands has nearly quadrupled over the past few days to as many as 13, a record number since China started sending ships to the region in September 2012 after Japan nationalized the islands' ownership.
Kishida told Chinese Ambassador Cheng Yonghua that the ships must leave the area, saying their presence has escalated tensions between the countries. He said their repeated infiltration and unilateral attempt to change the status quo were unacceptable.
The Japanese Coast Guard said at least two of the 13 Chinese vessels have been in the Japanese territorial waters around the islands despite repeated warnings for them to leave. Gun batteries were seen on several of the ships, officials said.
Cheng told reporters as he left the ministry that the increase in the China's coast guard fleet was to oversee the increased activity of the Chinese fishing boats. "Please understand that it's an effort by the Chinese side to avoid further complications to the situation."
Cheng said both sides need to make efforts through diplomatic dialogue to keep the situation under control. The ambassador also reiterated China's territorial claims to the islands.
Hundreds of Chinese fishing boats have also been seen accompanying the coast guard vessels, just as a fishing season in the East China Sea opens.
China also claims Japan-controlled Senkaku islands and calls them the Diaoyu islands.
Relations between Japan and China have long been strained over their wartime history, a sensitive topic during the summer because of end-of-the-war anniversaries.
Japanese media reports say the recent escalation in China's activity around the disputed islands may be seen as a warning against planned visits by members of Prime Minister Shinzo Abe's Cabinet to Tokyo's Yasukuni Shrine, which honors war criminals among the war dead, for the Aug. 15 anniversary to mark the end of World War II.