JAKARTA : China called on Indonesia Monday to release the crew of a Chinese fishing boat detained during a maritime confrontation, as Jakarta lodged a furious protest in the escalating row. The incident happened Saturday as Indonesian surveillance vessels tried to detain the trawler suspected of operating illegally near Indonesian islands in the South China Sea. After stopping the boat and removing eight crew members, the Indonesians were towing the vessel to shore when the Chinese coastguard appeared and rammed into the detained boat, helping to release it. However, Chinese foreigaan ministry spokeswoman Hua Chunying insisted Monday that the area near Indonesia's Natuna Islands was a "traditional Chinese fishing ground", and that the Chinese boat had to be rescued by coastguards after facing harassment from an Indonesian vessel.

The two nations normally enjoy good relations and the flare-up in tensions is rare.

Indonesia does not have overlapping territorial claims with China in the South China Sea, unlike other Asian nations. But it objects to China's "nine-dash line" defining its claims since this overlaps Indonesia's exclusive economic zone around the Natunas.

China's acting charge d'affaires in Jakarta, Sun Weide - who was summoned by both the foreign ministry and fisheries ministry Monday to hear protests - called for the release of the crew.

But Indonesian Fisheries Minister Susi Pudjiastuti, who is leading a tough campaign against illegal fishing in the vast archipelago, said the eight would face justice in Indonesia and dismissed as "baseless" Beijing's claim that the boat was operating in Chinese fishing grounds.

"I want China to show goodwill and return the boat, which has broken the law by carrying out illegal fishing," said Pudjiastuti, adding that authorities were considering filing a case to an international tribunal over the incident.

"With what took place yesterday, we feel our years-long efforts and work to promote peace in the South China Sea were interrupted and sabotaged."

Indonesia has in the past acted as a mediator in the region's disputes.

Earlier, Foreign Minister Retno Marsudi lodged a strong protest with Chinese embassy representatives, saying there had been a "violation by the Chinese coastguard of Indonesia's sovereign rights" and that Jakarta was seeking clarification about the incident.

While Indonesia does not have territorial disputes with China in the South China Sea, Jakarta is nervous about Beijing's growing assertiveness, and the military had already dispatched extra resources to the Natunas.

The navy said Monday it would double its patrols in the area. The Natunas are a string of islands rich in fish on the far northwest fringe of the archipelago.

Indonesia in 2014 launched a tough crackdown on illegal fishing which involves sinking foreign vessels caught fishing without a permit after impounding the boats and removing the crews.

Beijing voiced concern last year after Indonesia destroyed an impounded Chinese fishing vessel.

The nine-dash line is the demarcation Beijing uses on maps to demonstrate its claim to almost the whole of the South China Sea.