The presence of Chinese fishing boats poaching in the Natunas is a ruse by Beijing to stake its claims in the South China Sea, the naval commander of Indonesia's Western Fleet has said.

"Stealing our fish is just an excuse, it is really a move to establish their claims," said Rear-Admiral A. Taufiq R., referring to China. "When you claim a territory, you have to be there and their way to achieve that is by deploying fishing vessels."

His comments at a press conference yesterday came after Indonesian warships detained another China-flagged vessel and its crew last Friday, for fishing illegally in waters off the Natuna Islands.

China's claim of almost all of the South China Sea has brought it up against rival claims by Taiwan and Asean's Vietnam, the Philippines, Malaysia and Brunei. Indonesia is not a party to the disputes but grew concerned after Beijing in March said the waters around the Natunas, within Indonesia's exclusive economic zone, are part of its "traditional fishing grounds" and Chinese boats should be free to fish there.

On Friday's incident, the Indonesian navy said warning shots had to be fired to stop 12 Chinese fishing boats but it detained only the Yueyandong Yu 19038 and its crew of seven because it was the only boat with its fishing nets cast at the time.

Rear-Admiral Taufiq denied Beijing's allegation that shots fired by the Indonesian warship KRI Imam Bonjol had wounded a Chinese fisherman, calling it "baseless".

"The seven who were arrested are well, unharmed and unscathed. We fired warning shots only because they didn't stop," he said.

The Yueyandong Yu is the third Chinese boat caught poaching in Indonesian waters since March, said Maritime Affairs and Fisheries Minister Susi Pudjiastuti at a separate press conference yesterday.

The three are among 57 foreign fishing boats held by Indonesia for poaching since the start of this year, including from Vietnam and Malaysia. The ministry has sunk 176 fishing boats captured from poachers in the past eight months.

Ms Susi has vowed to continue to be tough with poachers, regardless of their flags, saying 16 more of such boats will be sunk after Ramadan next month. "A thief is a thief, (no matter) where they are from, Vietnam, China or Thailand," she said.

Beijing has condemned Indonesia's use of force and urged that it refrain from "any action that complicates or magnifies the dispute, or impacts the peace and stability of the region". President Joko Widodo has approved the setting up of a panel of international maritime law experts to find a way to amicably resolve the issue of China encroaching into Indonesian waters, said Coordinating Political, Legal and Security Affairs Minister Luhut Pandjaitan on Monday.

• Additional reporting by Wahyudi Soeriaatmadja