Manila (AFP) - China is using its fishing fleets with armed escorts to bolster maritime claims in disputed territory, a senior US State Department official warned Wednesday, calling China's behaviour "disturbing".
The comments came after Indonesian warships fired warning shots and detained a Chinese-flagged fishing boat and seven crew near the Natuna Islands in the South China Sea last week, in actions slammed by Beijing.
"I think it's a disturbing trend to see Chinese fishing vessels accompanied by coast guard vessels, used in a way that appears to be an attempt to exert a claim that may not be legitimate," said the US official via conference call to journalists in Southeast Asia.
"I do think that it does point to an expanding presence of Chinese -- sort of military and paramilitary forces -- and used in a way that is provocative and potentially destabilising," the US official, who asked not to be named, added.
Unlike several other countries in the region, Indonesia has no overlapping claims with China to islets or reefs in the sea, but Beijing's claim to fishing rights near the Natunas appears to overlap with Jakarta's exclusive economic zone.
Last week's incident was only the latest in a series of skirmishes between the two countries since Jakarta launched a crackdown on illegal fishing in 2014.
In March Chinese coastguards rammed a Chinese boat detained near the Natunas and helped it escape as the Indonesians towed the vessel to shore.
And last month, the Indonesian navy opened fire on a Chinese trawler near the islands and seized the vessel.
Following last week's confrontation, the commander of the Indonesian navy's western fleet said the fishing vessel incursions were "structured", indicating Beijing had "given its blessing".
"China protested because it thinks this area is theirs," commander Achmad Taufiqoerrochman told reporters.
"Actually the (fish) stealing is just a ruse to stake its claim," he said.
China has undertaken land-reclamation works in the Spratly Islands, one of the South China Sea's main archipelagoes which are also claimed by the Philippines, Brunei, Vietnam, Malaysia and Taiwan.
The US State Department official said Washington hoped a pending ruling by a United Nations-backed tribunal on South China Sea maritime entitlements will push rival claimants into talks.
The case was lodged by the Philippines against China in 2013 to challenge Beijing's "nine-dash line" map through which it claims to control nearly all of the strategic and reputedly resources-rich waters.
"It is in China's interest not to take any action that would be provocative and directly in contradiction to the ruling," the US official said.