BEIJING (AFP) - Top US diplomat John Kerry is to meet Chinese leaders on Saturday, with State Department officials saying he would take a tough line over Beijing's island-building in strategic but disputed waters.
The US is weighing sending warships and surveillance aircraft within 12 nautical miles - the normal territorial zone around natural land - of artificial islands that Beijing is building in the South China Sea.
Such a move could lead to standoff on the high seas between the world's top two economies in an area home to vital global shipping lanes and believed to be rich in oil and gas deposits.
Pentagon officials last week revealed that China is building artificial islands on top of coral reefs at an unprecedented pace, in a land reclamation effort dubbed a "great wall of sand" by one American commander.
The rapid construction comes to 800 ha, with 75 per cent of the total created in the last five months alone.
Senior State Department officials said ahead of the talks in Beijing that Kerry would "reinforce... the very negative consequences on China's image, on China's relationship with its neighbours, on regional stability, and potentially on the US-China relationship" of Beijing's activities in the sea.
Beijing claims nearly all of the South China Sea, even waters close to the coasts of other littoral states, on the basis of a segmented line dating back to Chinese maps of the 1940s.
One official said Kerry would "leave his Chinese interlocutors in absolutely no doubt that the United States remains committed to maintain freedom of navigation".
"That's a principle that we are determined to uphold," the official added.
US officials increasingly believe Washington needs to send a clear signal about China's dredging activities around the Spratly Islands and other disputed territories, though they want to calibrate any military operation to avoid triggering a crisis.
They also stress that under the UN Convention on the Law of the Sea only natural land masses create a territorial claim, not artificial islands.
"You can't build sovereignty," an official said.
But the US has never ratified the convention itself.
Beijing defends the island-building as taking place within its own territory and intended to enhance its ability to carry out international obligations such as search and rescue.
In a commentary ahead of Saturday's talks, China's official news agency Xinhua said the US was guilty of "thinly veiled hypocrisy".
"The United States is not a party in the South China Sea disputes, which are between China and other claimants and should be handled by those directly involved," it said.
"Washington has no valid grounds whatsoever to point an accusing finger at Beijing over South China Sea. Instead, it needs to look at itself in the mirror," it said.
It accused the US of seeking "a pretext to maintain its hegemonic presence in the region".
The US is in the process of a foreign policy "pivot" to Asia and Australian Prime Minister Tony Abbott on Friday denied the Washington planned to base B-1 bombers in his country, saying an American official had "misspoken" when he told the Senate the deployment was intended.
Chinese President Xi Jinping is due to carry out a state visit to the US in September.