China has deployed a fourth-generation SAM system from Woody island in the South China Sea.
The satellite imagery taken on 14 February indicates that China deployed two batteries of eight missile launchers and a radar system from the island.
Despite the location positioned within the 200nm zone of China, Woody island has been subject of a territorial dispute between China, Taiwan and Vietnam for years.
IHS Jane's Neil Ashdown said: "It is probable that the deployment was intended to send a message to the US and other claimants in the South China Sea, in the wake of freedom of navigation operations conducted by US naval vessels in October 2015 and January 2016."
US Secretary of State John Kerry said the US expects to have a 'very serious conversation' with China over the issue.
Kerry added: "There is every evidence, every day, that there has been an increase of militarisation from one kind or another. It's a serious concern."
The move follows the recent sail of the USS Curtis Wilbur, a US Navy guided missile destroyer which navigated within 12 miles of Triton Island in the South China Sea to contest Chinese territorial claims.