China repeats apology demand after Japan frees fisherman

China pushed its demand for an apology from Japan for detaining a Chinese fishing trawler captain, showing no sign of an end to the row after Japan released the captain and said no apology was necessary.

The dispute illustrates the fragility of ties between Asia's two biggest economies troubled by Chinese memories of Japanese wartime occupation and territorial disputes over parts of the East China Sea that could hold rich reserves of gas.

Tokyo came under criticism from domestic media for "caving in" to Chinese pressure by releasing the captain after China detained four Japanese citizens, although Japanese officials have denied the linkage.

The four were detained on suspicion of violating the law regarding protection of Chinese military facilities, though the exact offence was not clear.

Fishing trawler captain Zhan Qixiong arrived back in China on Saturday after his boat collided with Japanese patrol ships on Sept 7 near disputed islets, known as the Diaoyu in Chinese and Senkaku in Japanese. His trawler and crew had earlier been released.

China demanded an apology and compensation, a request Japan said on Saturday was "groundless".

"Japan's actions have severely infringed upon China's territorial sovereignty and the personal rights and interests of a Chinese citizen, so of course China has the right to demand an apology and compensation from Japan," Chinese foreign ministry spokesperson Jiang Yu said in remarks posted on the ministry's website late on Saturday.

Japan's former foreign minister said international perceptions of China would be hurt by its refusal to back down.

"It was our territory and there was no fault in arresting him in accordance with the law," Katsuya Okada, secretary-general of the ruling Democratic Party and foreign minister until a September 17 cabinet reshuffle, told public broadcaster NHK on Saturday.

"There have been views that this affair was a complete defeat for Japan, but this was a loss for China. China showed the world what kind of a country it is."

Okada again said Japan could not accept the demand for an apology and compensation.

Freed captain Zhan told China Central Television he was eager to return for more fishing near the islands.