Japan has said it is investigating whether online video clips that appear to show a Chinese fishing boat colliding with Japanese patrol vessels are authentic.
The collision in September near disputed isles in the East China Sea, the site of vast potential gas and oil reserves, sparked a diplomatic spat between the two Asian giants.
Japan detained the Chinese skipper of the trawler, which made him a hero in China.
The clips were posted on the video sharing website YouTube early on Friday, threatening to reignite the China-Japan row.
Naoto Kan, the embattled Japanese prime minister, has faced heavy criticism domestically for freeing the captain and tensions between the two countries have chilled since the incident.
"We need to look into the authenticity of such clips," Yoshito Sengoku, the chief cabinet secretary, told a news conference.
Japanese TV news programmes also aired the video clips, which showed a blue boat bearing a Chinese name colliding with two patrol boats as sirens blared and Japanese crew shouted "halt".
"Generally speaking, if documents in a criminal suit have been released on YouTube and to the public, then that is a ... grave situation for investigation authorities," Sengoku added.
Japanese prosecutors released the captain but are still technically investigating whether to charge him.
Sengoku said China had inquired about the videos through a diplomatic route, and added that he hoped Kan and Hu Jintao, the Chinese president, would meet bilaterally at the Asia-Pacific Economic Cooperation (APEC) summit in Yokohama, near Tokyo, next weekend.
|Released Chinese boat captain Zhan Qixiong received a hero's welcome up his return to his home country [AFP]
The government had released the video for viewing by a small number of legislators but refused to make it public for fear of inflaming anti-Chinese sentiment.
Japan's opposition Liberal Democrats threatened to delay a 4.4 trillion yen ($54.51bn) extra budget for the fiscal year to March 31 over the government's handling of the matter.
"This issue is related to national interests and sovereignty, so if the video is not released (to the public), I am not sure what will happen to the extra budget deliberation," Nobuteru Ishihara of the Liberal Democratic Party told reporters.
Tokyo, Washington and Southeast Asian nations have grown increasingly wary of a rising China's intentions as it spends heavily to modernise its military, sends its navy further afield and asserts sovereignty over the contested South China Sea.
Beijing this week attempted to calm the fears.
"China's overall national strength is rising rapidly, and this is making an important contribution to promoting Asia's peace and prosperity, global economic growth, and reform of the international financial system," Hu Zhengyue, the Chinese assistant foreign minister, told the official Xinhua news agency.
Beijing has staunchly asserted its sovereignty over the islands, known as Senkaku in Japan and Diaoyu in China, and stressed that the video would not alter its stance in the feud.
"It was illegal for the Japanese coast guard vessels to interfere with, chase, block, surround and seize the Chinese fishing boat in the seas off the Diaoyu islands," Ma Zhaoxu, a Chinese foreign ministry spokesman, said.
"The so-called video cannot alter the truth of the matter, and cannot disguise the illegality of the Japanese actions."