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TOKYO (AP) — Japan freed 14 crew members of a Chinese fishing ship Monday nearly a week after their vessel and two Japanese patrol boats collided near disputed southern islets. But China lashed out at Tokyo's decision to keep the captain in custody.

Such collisions or close calls in disputed waters have frequently touched off nationalistic protests among the broader population about sovereignty and complicate efforts to improve ties between China and Japan — wary neighbors that are the world's second- and third-largest economies and major trading partners. Beijing has said the confrontation could damage its relations with Japan, underlining the sensitivity of the territorial dispute in the East China Sea.

The dispute has sparked anti-Japanese activists in China and Taiwan, which also claims the islands in question, to sail to the area on their own protest missions — although both governments have sought to rein them in so as not to inflame tensions further.

Japanese authorities sought to ease tensions Monday by allowing the 14 crew members to board a Chinese chartered plane that was sent to pick them up from a nearby Japanese island, said the Foreign Ministry. The Kyodo News Agency also reported that Japanese Prime Minister Naoto Kan urged both sides on Monday to work hard to improve their ties.

But Japan continues to detain the captain of the Chinese trawler, Zhan Qixiong. A Japanese court has granted prosecutors permission to keep the captain in custody until Sept. 19 to decide whether to formally indict him.

Tokyo sees this as its right but Beijing sees as provocation to its claim for sovereignty over the East China Sea islands, called Diaoyu or Diaoyutai Islands in Chinese or the Senkakus in Japanese. Located about 120 miles (190 kilometers) east of Taiwan, the islands are controlled by Japan, but also claimed by Taiwan and China.

"China expresses strong dissatisfaction with and grave protest against Japan's obstinate decision to put the Chinese captain under the so-called judicial procedures," said Foreign Ministry spokeswoman Jiang Yu. "Japan will reap as it has sown, if it continues to act recklessly."

The incident has provoked a strident response from Beijing, which said Friday it was postponing talks scheduled earlier with Japan on contested undersea deposits in the East China Sea. On early Sunday, China's State Councilor Dai Bingguo called in Japanese Ambassador Uichiro Niwa — the fourth time that he has been summoned over the incident.

While worried about appearing weak in front of a nationalistic public, China's communist leadership has also tried to rein in activists to prevent any patriotic displays from spiraling beyond its control.

On the Chinese mainland, one activist said he abandoned a plan to sail to the islands after being harassed by plainclothes police officers in the port the Jingiang, where the detained boat captain is from.

"They followed me around everywhere, so my plans for renting a boat in Fujian to sail to the Diaoyu were scrapped and I left that night," said Qiu Haitang, the online name for an auto parts industry worker who did not want his real name used, in a telephone interview. "They didn't tell me I had to leave, but it was definitely the impression they gave by following me everywhere — that I was not welcome there."

In Xiamen, about a dozen other activists said they waited in port for a second day unable to set sail.

"On the surface, the Chinese government is saying that it won't support or oppose or ban these protest actions organized by civic groups. But they are threatening boat owners so they are afraid of setting sail," Lo Chau, a Hong Kong activist with the group, told Hong Kong reporters in Xiamen.

Activists in Hong Kong are passionate about the issue because they feel the Japanese claim over the islands is an extension of lingering Japanese imperialism that has resisted remorse and reparations for World War II atrocities, said legislator Albert Ho.

Meanwhile, three Taiwanese activists set out by sea Monday to promote Taiwan's claim to the islands. The Taiwanese coast guard barred six activists from Hong Kong from joining their trip.

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Associated Press Writers Peter Enav in Taipei, Min Lee in Hong Kong and Ch-Chi Zhang in Beijing contributed to this report.