At least nine Japanese activists swam ashore to the uninhabited island early on Sunday, in a move expected to inflame tensions between Asia's two biggest economies. The nine activists reportedly raised a Japanese flag before swimming back to their boats. They were later questioned by Japanese Customs officials.

They were part of a flotilla of more than 100 Japanese nationals who sailed to the island, which is part of an archipelago in the East China Sea. The group included several members of parliament and local lawmakers.

For decades China and Japan have been engaged in a feud over the island chain, which both nations claim as their own. The archipelago, known in Japan as Senkaku and as Diaoyu in China, is near potentially rich gas reserves.

In a bid to ease tensions, Japan deported a group of 14 Chinese activists on Friday who were detained after several managed to land on the islands after sailing from Hong Kong. They were the first non-Japanese citizens to set foot on any part of the archipelago since 2004.

China issues warning

On Saturday Beijing warned Japan against taking any action that "seeks to undermine China's territorial sovereignty."

"China reiterates that any unilateral action taken by Japan regarding the islands are illegal and invalid", a foreign ministry statement said, adding that any such actions would not undermine its claim over the territory.

Meanwhile, a Japanese ruling party member has advised his country to expand its coastguard to defend the islands.

"Coastguard officials are doing their best, and so the government and the ruling parties will discuss how to strengthen our backup to them," Seiji Maehara, the policy chief of the Democratic Party of Japan, told reporters on Saturday.

The renewed dispute came as tensions also rose between Japan and South Korea after President Lee Myung-Bak visited uninhabited islets controlled by Seoul but claimed by Tokyo.

cpp/av (AFP, Reuters)