Japan has agreed to buy a group of islands disputed with China from their private owners, a government official said on Monday, prompting an angry rebuke from China a day after Chinese President Hu Jintao warned against such an "illegal" move.

Japan aimed to nationalize the uninhabited islands in the East China Sea as soon as possible to control them in a peaceful and stable manner, Chief Cabinet Secretary Osamu Fujimura said.

The islands, called Senkaku in Japan and Diaoyu in China, are near rich fishing grounds and potentially huge maritime gas fields and have been at the heart of long-running territorial disputes between the world's second and third-largest economies.

Tension flared anew last month when Japan detained a group of Chinese activists who landed on the islands. But the row may now be having an economic impact, intensifying from merely an exchange of rhetoric, with a Chinese official saying Japanese car sales may have been hit in the world's biggest auto market.