A court case against a group of Chinese fishermen facing jail in the Philippines for poaching was postponed for a third time on Wednesday, after the government accused China of frustrating the proceedings.

The fate of the nine fishermen has worsened an already bitter row between the Philippines and China over competing territorial claims in the South China Sea, because they were arrested last month in disputed waters.

A court on the westernmost Philippine island of Palawan that is meant to hear the case on Wednesday postponed the pre-trial hearing until July 1 after their lawyer appealed for more time, prosecutor Alen Rodriguez told AFP.

The pre-trial hearing was initially scheduled for June 4, but has now been postponed three times.

The proceedings had previously been postponed due to the court's inability to find an interpreter for the Chinese.

President Benigno Aquino's spokesman said on Tuesday the Chinese embassy in Manila was partly to blame for the delays by not assisting in providing an interpreter.

"Chinese embassy officials don't want to participate in the proceedings. They don't want to provide an interpreter for the Chinese fishermen," spokesman Herminio Coloma said, citing comments from Rodriguez.

Local ethnic Chinese residents have in the past acted in similar cases. One of those residents initially translated for the fishermen at their arraignment hearing last month, but then withdrew his services.

Some of the ethnic Chinese residents told AFP that, after meeting a Chinese diplomat, they decided not to work on the case because they felt intimidated and did not want to antagonise the Chinese government.

However a young ethnic Chinese resident was finally persuaded to act as an interpreter, according to Rodriquez, and helped the fishermen at Wednesday's proceedings.

A Chinese embassy spokesman did not respond to requests for comment.

The Chinese government has previously said it does not recognise the case and demanded the fishermen be released immediately, insisting they were fishing legally in waters belonging to China.

Police detained the fishermen on May 6 near Half Moon Shoal in the South China Sea, 111 kilometres (69 miles) off Palawan.

They were charged with poaching an endangered species, which carries a maximum jail term of 20 years, after hundreds of turtles were allegedly found on their boat.

The Philippines insists it has sovereign rights to the shoal, which is part of its exclusive economic zone and more than 1,000 kilometres from the nearest major Chinese landmass.

But China claims nearly all of the South China Sea, even waters approaching the coasts of its neighbours.

The dispute has severely strained relations in recent years, with the Philippines accusing China of embarking on an "expansionist agenda" that has included creating artificial islands in areas close to the Philippines.

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