TOKYO - Japan summoned the Chinese ambassador on Wednesday as a diplomatic row flared over a remote chain of islands, with Beijing asserting its "indisputable sovereignty" to the uninhabited territory.
The row erupted after three Chinese patrol boats approached the islands, and led China's foreign minister, meeting with his Japanese counterpart at a forum in Cambodia, to insist the islands had been Chinese "since ancient times".
The dispute, which centres around islands in the East China Sea known as Senkaku in Japanese and Diaoyu in Chinese, is the latest such territorial spat involving China and its neighbours.
The Japanese coastguard said the Chinese vessels entered Japanese waters around the islands early Wednesday.
"It is clear that historically and legally Senkaku is an inherent territory of Japan," top government spokesman Osamu Fujimura told a press briefing.
The crews of the vessels, which had since left the islands' immediate vicinity, initially rebuffed Japanese orders to leave.
"We are conducting official duty in Chinese waters. Do not interfere. Leave China's territorial waters," the crews said, according to the coastguard.
Chinese foreign ministry spokesman Liu Weimin rejected Tokyo's summoning of its ambassador, telling reporters in Beijing: "China does not accept Japanese representations over this."
In Phnom Penh, Chinese Foreign Minister Yang Jiechi met Japanese counterpart Koichiro Gemba and "reaffirmed China's principled position" on the islands, according to a statement from the Chinese delegation.
"He stressed that Diaoyu Islands and their affiliated islets have always been China's territory since ancient times, over which China has indisputable sovereignty," it said.
The islands lie in rich fishing grounds and it is thought they may also contain valuable mineral reserves. Tokyo recognises a private Japanese family as their owner and the city government has said it plans to buy the islands from them.
The waters around the disputed islands have been the scene of previous territorial spats, including the arrest of a Chinese trawlerman in late 2010 when he rammed his boat into two Japanese patrol boats.
Yang's meeting with Gemba came at a gathering of the Association of Southeast Asian Nations (ASEAN) meant to address some of the recent frictions over competing territorial claims in the resource-rich South China Sea.
The 10 members of Southeast Asian regional body ASEAN have been trying to agree a long-stalled "code of conduct" for the disputed area to help settle overlapping claims.
The Philippines is leading a push for ASEAN to unite to persuade China to accept a code based on a UN law on maritime boundaries that would delineate the areas belonging to each country.
Manila also wants ASEAN to condemn a standoff last month between Philippine and Chinese ships over Scarborough Shoal, an outcrop in the South China Sea.
Beijing also recently angered Vietnam by inviting bids for exploration of oil blocks in contested waters, sparking protests in Hanoi.
China's assertiveness over disputed territories in the South China Sea, which also contains vital shipping lanes, is seen by analysts as pushing anxious neighbouring countries closer to the United States.
US Secretary of State Hillary Clinton earlier arrived in Cambodia to press for closer relations with ASEAN as part of Washington's strategy of "pivoting" towards Asia to challenge China's influence.
She is to take part in the ASEAN Regional Forum on Thursday, which brings together 26 nations and the European Union.