China on Thursday again urged Japan to immediately set free the Chinese trawler captain who was detained last week near the Diaoyu Islands, saying the detention is "a protruding obstacle" to Sino-Japanese ties.

Foreign Ministry spokesperson Jiang Yu made the remarks at a regular press briefing, urging Japan "to take concrete actions to remove the obstacle."

Two Japan Coast Guard patrol ships and the Chinese fishing boat collided last week in waters off the Diaoyu Islands. Japan is still holding Zhan Qixiong, the trawler's captain, which China claims is illegal.

"The current situation was caused by what Japan has done on the Diaoyu Islands, so Japan should completely accountable for it," she said.

She reiterated that the Diaoyu Islands were Chinese territory since ancient times.

"China possesses indisputable sovereignty over the Diaoyu Islands and China's willingness and determination to safeguard its sovereignty and territorial integrity is unshakable," she said.

China had stated its solemn stance to Japan time and again through different channels, she said.

Media reports said Japan had warned nationals living or working in China to exercise caution. Jiang said she believed the Chinese people "can express their ideas by rational and legal means."

"The Chinese government will continue to protect the safety of foreign organizations and people in China, including those from Japan," she said.

After China lodged representations with Japan, all the crew, except the captain, returned to the southeastern city of Fuzhou on a flight chartered by the Chinese government Monday. The trawler returned Wednesday.

Jiang said people should remember and learn from history, and look at the future on the basis of history.

She was referring to the September 18 Incident of 1931, when Japanese troops blew up a section of the Dalian-Harbin Railway near Shenyang, and then accused the Chinese troops of sabotage as a pretext to bombard the barracks of the Chinese troops near Shenyang the same day, thus starting a massive armed invasion of northeastern China. Japan then launched an all-out invasion of China in the ensuing 14 years.

"China hopes Japan can have a correct view and proper handling of the history, and take concrete steps to stick to a path of peaceful development," Jiang said.