In a phone call on Wednesday with his Philippine counterpart Gilberto Teodoro, Austin “reaffirmed the ironclad US commitment to the Philippines” following Chinese obstruction at the Second Thomas Shoal “of a lawful Philippine resupply mission,” said a statement from the Pentagon.

Austin emphasised support for the Philippines in defending its sovereign rights and jurisdiction, it said.

The Philippines routinely sends boats to the Second Thomas Shoal to deliver supplies to a small group of its soldiers posted to guard a warship that was intentionally grounded on a reef 25 years ago.

The Philippines has been furious over what it calls repeated aggression by China’s coastguard around disputed features located inside Manila’s 322km exclusive economic zone.

China warned the Philippines on Monday to behave cautiously and seek dialogue, saying their relations were at a “crossroads” as confrontations between their coastguards over maritime claims worsened tensions.

China, which claims almost the entire South China Sea, has accused the Philippines of encroaching on its territory and says it took necessary measures against the vessels. It has told the United States not to interfere.