China has deployed surface-to-air missiles on a disputed island in the South China Sea, Taiwan says.
Satellite images taken on 14 February appear to show two batteries of eight missile launchers and a radar system on Woody or Yongxing Island in the Paracels.
The presence of missiles would significantly increase tensions in the acrimonious South China Sea dispute.
China’s Foreign Minister Wang Yi said reports were a Western media invention.
But Mr Wang defended “the limited and necessary self-defence facilities” on islands inhabited by Chinese personnel as “consistent with the right for self-preservation and self-protection…. under the international law”.
Taiwan’s defence ministry said it had “learned of an air defence missile system deployed” by the Chinese on Woody Island.
It would not say how many missiles had been deployed or when, but told the BBC they would be capable of targeting civilian and military aircraft..
The commander of the US Pacific Fleet confirmed the deployment to Reuters news agency.
Adm Harry Harris said such a move would be “a militarisation of the South China Sea in ways” China’s President Xi Jinping had pledged not to make.
Japan’s Chief Cabinet Secretary Yoshihide Suga said there were “serious concerns” over China’s “unilateral move to change the status quo” in the region, and “we cannot accept this fact”.
China has been carrying out extensive land reclamation work in the region, which it says is legal and for civilian purposes.
But the work has angered other countries which also claim the territory, and there is growing concern about the implications of the area becoming militarised.
The latest images of Woody Island were captured by Image Sat International.
They show a close-up of a section of beach, the shape of which resembles the northern coastline as it appears on other images, and point out two missiles batteries. Each battery is made up of four launchers and two control vehicles.
Two of the the launchers appear to have been erected, says the report.
An image taken of the site on 3 February shows the beach empty.
Fox News quoted a US defence official as saying the missiles appeared to be the HQ-9 air defence system, with a range of about 200km (125 miles).
The news comes as South East Asian regional leaders end a two-day meeting in California where South China Sea had been a topic of debate.
US President Barack Obama said the members had discussed the need for “tangible steps” to reduce tensions, including “a halt to further reclamation, new construction and militarization of disputed areas”.
A Pentagon spokesman said the US could not comment on intelligence matters but watched such issues “very closely”.
“The United States continues to call on all claimants to halt land reclamation, construction, and militarization of features in the South China Sea,” he said in a statement to the BBC.