The US has seen Chinese activity around a reef China seized from the Philippines nearly four years ago that could be a precursor to more land reclamation in the disputed South China Sea, the US Navy chief says.
The head of US naval operations, Admiral John Richardson, expressed concern that an international court ruling expected in coming weeks on a case brought by the Philippines against China over its South China Sea claims could be a trigger for Beijing to declare an exclusion zone in the busy trade route.
Richardson told Reuters the United States was weighing responses to such a move.
China claims most of the South China Sea, through which more than $5 trillion in global trade passes every year. Vietnam, Malaysia, Brunei, the Philippines and Taiwan have rival claims.
Richardson said the US military had seen Chinese activity around Scarborough Shoal in the northern part of the Spratly archipelago, about 200km west of the Philippine base of Subic Bay.
Richardson said China's pursuit of South China Sea territory, which has included massive land reclamation to create artificial islands elsewhere in the Spratlys, threatened to reverse decades of open access and introduce new "rules" that required countries to obtain permission before transiting those waters.
He said that was a worry given that 30 per cent of the world's trade passes through the region.
China could respond to the ruling by the court of arbitration in The Hague by declaring an air defence identification zone, or ADIZ, as it did farther north in the East China Sea in 2013.
The United States planned to continue carrying out freedom-of-navigation exercises within 12 nautical miles of disputed South China Sea geographical features to underscore its concerns about keeping sea lanes open.
Richardson said the United States would welcome the participation of other countries in joint patrols in the South China Sea, but those decisions needed to be made by the countries in question.
He said the US military saw good opportunities to build and rebuild relationships with countries such as Vietnam, the Philippines and India, which have all realised the importance of safeguarding the freedom of the seas.
But he said Washington needed to proceed judiciously rather than charging in "very fast and very heavy," given the enormous influence and importance of the Chinese economy in the region.
"We have to be sophisticated in how we approach this so that we don't force any of our partners into an uncomfortable position where they have to make trade-offs that are not in their best interest," he said.
"We would hope to have an approach that would ... include us as a primary partner but not necessarily to the exclusion of other partners in the region."
© RAW 2016