TOKYO - China demanded an apology and compensation from Japan on Saturday after it released a Chinese fishing boat captain held more than two weeks after a collision near disputed islands that has triggered the worst spat between the Asian neighbours in years.

Japanese authorities released Zhan Qixiong, 41, early Saturday morning and he was flown home by chartered plane to Fuzhou, the capital of China's southeastern Fujian province, the offical Xinhua News Agency reported.

Though his release is intended to defuse a diplomatic spat sparked when Japan arrested the captain after his trawler collided with two Japanese patrol boats near islands in the East China Sea claimed by both countries, tensions remain high.

China's Foreign Ministry issued a statement repeating its "strong protest" that the boat crew had been detained and sought an apology from Japan.

"It is unlawful and invalid for Japan to detain, investigate or take any form of judicial measures against the Chinese fishermen and trawler. The Japanese side must make an apology and compensation for this incident," the statement said.

Zhan's release came after intense pressure from China, which suspended ministerial-level dialogue with Tokyo and postponed talks on developing disputed undersea gas fields. Earlier this week, Chinese Premier Wen Jiabao had sternly threatened "further action" against Japan if it did not immediately release the captain.

On Friday, Japanese Prime Minister Naoto Kan, who was in New York for a U.N. summit also attended by Wen, called for calm discussions between China and Japan in the wake of the tense territorial spat.

But an editorial Saturday in Japan's nationally circulated Yomiuri newspaper criticized the captain's release as "a political decision that put the mending of relations as a priority" and urged the Japanese government to fully explain its decision to the people.

"Needless to say, the Senakaku Islands are part of Japan's territory. The government must continue to assert this view both domestically and abroad," it said.

Zhan was arrested on Sept. 8 after the collision off the uninhabited chain of islands called Diaoyu or Diaoyutai in Chinese and Senkaku in Japanese. Located 120 miles (190 kilometres) east of Taiwan, the islands are controlled by Japan, but also claimed by Taiwan and China.

Prosecutors had detained and questioned the captain while they decided whether to press charges. His 14-member crew and ship were returned to China.

The captain's arrest, and the territorial dispute behind it, stirred nationalistic sentiment in China and Japan and threatened to undermine business ties between their intertwined economies -- the world's second- and third-largest.

On Thursday, Beijing said it was investigating four Japanese suspected of illegally filming military targets and entering a military zone without authorization. Also, there were reports China had suspended Japan-bound shipments of rare earth metals crucial in advanced manufacturing.

Fujita Corp., a Japanese construction company, confirmed Friday that four of its Japanese employees were being questioned by Chinese authorities. The company said the men were working to prepare a bid for a project to dispose of chemical weapons abandoned in China by the Japanese military during World War II.

Chinese authorities accuse the men of entering a military zone without authorization.

Meanwhile, Japanese trading company officials said that starting Tuesday, China had halted exports to Japan of rare earth elements, which are essential for making superconductors, computers, hybrid electric cars and other high-tech products. Japan imports 50 per cent of China's rare earth shipments.

China's Trade Ministry denied reports that Beijing is tightening curbs on exports of rare earths to Japan, but Japan's trade minister, Akihiro Ohata, said he has "information" that China's exports to some Japanese trading houses have been stopped.

It is also one of several territorial spats straining China's ties with its Asian neighbours while its increasingly powerful navy enforces claims in disputed waters. Washington has signalled its intention to protect its interests in those waters and to keep them open for commerce, drawing China's irritation by urging it to resolve the disputes.

The U.S. praised Japan's decision to release the captain. State Department spokesman P.J. Crowley told reporters Friday that the U.S. hopes the decision will ease tensions between the two longtime Asian rivals.

This is "how mature states resolve these things, through diplomacy," Crowley said. He says the United States continues to support freedom of navigation in Asia.

Earlier, prosecutors in Okinawa, southern Japan, where the 41-year-old captain had been held, said they would let him go partly because they did not perceive any premeditated intent to damage the Japanese coast guard boats -- but also for diplomatic reasons.

"We have decided that further investigation while keeping the captain in custody would not be appropriate, considering the impact on the people of our country, as well as the Japan-China relations in the future," said Toru Suzuki of the Naha, Okinawa, prosecutors office.

Authorities in Okinawa also said they wouldn't officially close the case -- leaving room for some ambiguity that would allow both countries to save face.

"The Japanese government had to balance the Japanese people's feelings about the territorial issue and those of China and Taiwan and seek a win-win scenario which is to be ambiguous," said Takehiko Yamamoto, an international politics professor at Waseda University in Tokyo.

But others, including Tokyo's outspoken governor, Shintaro Ishihara, said Japan had caved in to Chinese pressure. "The government made an incredibly wrong decision in this case," he said.

Comments left on popular Japanese online communities were largely critical of the move.

Liu Jiangyong, a professor with Institute of International Studies at Tsinghua University in Beijing, called the release a "wise decision" by the Japanese government that could even lead to stronger ties.

"The decision may become a turning point for the improvement of relations between the countries, and both sides should grasp the opportunity to get relations back to the correct track," Liu said.