By David Brunnstrom and Ben Blanchard
The US has accused China of raising tensions in the South China Sea by its apparent deployment of surface-to-air missiles on a disputed island.
US State Department spokesman John Kirby said commercial satellite imagery suggested "very recent" placement of missiles on Woody Island in the Paracel island chain that went against China's pledge not to militarise the South China Sea.
"The Chinese have said one thing, and yet appear to be doing another," Kirby told a regular news briefing on Thursday (local time).
"We see no indication that ... this militarisation effort, has stopped. And it's doing nothing ... to make the situation there more stable and more secure. In fact, it's having quite the opposite effect."
On Wednesday, US Secretary of State John Kerry said the US would have "very serious" talks with China about militarisation of the South China Sea.
China has offered little specific response to the missile deployment reports, which first appeared on Fox News on Tuesday, but has accused Western media of "hyping up" the story and said China had a legitimate right to military facilities on territory it views as its own.
China claims most of the South China Sea, through which more than US$5 trillion in global trade passes every year.
Vietnam, Malaysia, Brunei, the Philippines and Taiwan have rival claims.
Australian Foreign Minister Julie Bishop, the first senior Western official to visit China since the reports appeared, said she raised the issue of the South China Sea's militarisation in talks in Beijing on Thursday.
She told reporters after meeting China's top diplomat, State Councillor Yang Jiechi, that China had "challenged" the deployment report but had neither denied nor admitted that the missiles were there.
"So until such time as we have a clear picture of it, of course it's a matter of concern," she said.
Bishop referred to comments by Chinese President Xi Jinping in Washington last year that China did not intend to militarise islands in the South China Sea, and added: "We certainly hold China to that and that's been reiterated to me."