A Chinese envoy called on Indonesia Monday to release eight crew members of a Chinese fishing boat detained during a maritime confrontation, after he was summoned by furious Indonesian ministers.
Jakarta says Indonesian vessels were on Saturday trying to detain a Chinese fishing boat operating illegally near Indonesia's Natuna Islands in the South China Sea, when they were prevented from doing so by Chinese coastguard vessels.
However Sun Weide, China's acting charge d'affaires in Jakarta, insisted that the incident occurred in "traditional Chinese fishing grounds".
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 it overlaps Indonesia's exclusive economic zone around the Natunas.
Eight crew members of the Chinese fishing vessel were detained before the coastguards intervened, Sun said, and urged Jakarta to let them go.
"I asked the minister to release eight fishermen detained by Indonesia," he told reporters after being summoned by Fisheries Minister Susi Pudjiastuti, who has been leading a crackdown on illegal fishing.
Foreign Minister Retno Marsudi also summoned Sun and lodged a strong protest, saying that the Chinese coastguards had entered Indonesian waters during the confrontation.
"There was a violation by the Chinese coastguard of Indonesia's sovereign rights and jurisdiction in the exclusive economic zone and continental shelf," she told reporters, reading the protest she had lodged with him.
The foreign minister said Jakarta had asked for clarification from the Chinese government about the incident.
Sun was summoned because the ambassador is currently in Beijing.
Indonesia in 2014 launched a tough crackdown on illegal fishing which involves sinking foreign vessels caught fishing without a permit in its vast waters, after impounding the boats and removing the crews.
Beijing voiced concern last year after Indonesia destroyed an impounded Chinese fishing vessel.
The Natunas are a string of islands rich in fish on the far northwest fringe of the Indonesian archipelago.
In Saturday's incident, a Chinese coastguard boat initially collided with the Chinese fishing boat as it sought to intervene. A larger Chinese coastguard vessel then arrived and the Indonesians abandoned efforts to detain the fishing boat.
The nine-dash line is the demarcation Beijing uses on maps to demonstrate its claim to almost the whole of the South China Sea.
Tensions in the sea -- through which one-third of the world's oil passes -- have mounted in recent months since China transformed contested Spratly reefs into artificial islands capable of supporting military facilities.