TOKYO (AFP) -- Japan summoned the Chinese ambassador Wednesday as a diplomatic row flared up after three Chinese patrol boats approached a chain of islands at the centre of a bitter territorial dispute.

The Japanese coastguard said the vessels entered Japanese waters around the islands in the East China Sea known as Senkaku in Japanese and Diaoyu in Chinese early Wednesday.

That prompted Japan’s Foreign Ministry to summon the Chinese ambassador in protest, said Chief Cabinet Secretary Osamu Fujimura.

“It is clear that historically and legally Senkaku is an inherent territory of Japan,” the government’s top spokesman told a regular press briefing, adding that Beijing’s envoy had been summoned over the vessels.

The trio of Chinese ships were identified as Yuzheng 35001, Yuzheng 204 and Yuzheng 202, the coastguard said.

The crew of the vessels, which have 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.

The incident comes amid increasingly sore relations over the islands, which lie in rich fishing grounds and may contain valuable mineral reserves, with Tokyo earlier saying it may buy the chain from their private Japanese owner.

The Tokyo metropolitan government said it had already collected more than 1.3 billion yen ($16.3 million) in donations from across the country to fund the purchase.

Beijing has shot back that Japan has no right to buy the islands.

Japanese and Chinese foreign ministers were expected to meet later Wednesday on the sidelines of an Association of Southeast Asian Nations forum in Phnom Penh.

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.

The latest chapter in the ongoing row comes as a separate report in Japan’s top-selling Yomiuri Shimbun newspaper implicated a senior member of China‘s People’s Liberation Army in a cyberattack on Japan’s parliament last year.

An e-mail address tied to the unnamed man was allegedly used as a destination for stolen data from the attack which reports had earlier said were launched from a China-based server.