China may be installing a high-frequency radar system in the disputed Spratly Islands, a US think tank has reported, citing satellite imagery analysis.
Images showed near-complete construction of radar facilities at the Cuarteron Reef near the Philippines, the Asian Maritime Transparency Initiative at Washington's Center for Strategic and International Studies said.
"Two probable radar towers have been built on the northern portion of the feature, and a number of 65-foot (20-meter) poles have been erected across a large section of the southern portion," the report said.
Higher frequency radars can track down stealth aircraft in its range and analysts have said the new installation could put American and allied stealth aircraft at risk.
The report also says the area of the artificial island has now expanded to about 52 acres.
China's land reclamation and the building of military installations and air strips on them have been sharply criticized by the United States and its allies in the Pacific Rim.
The poles erected on the island could be a high-frequency radar installation, the agency said, adding that the system will significantly bolster China's ability to monitor surface and air traffic across the southern portion of the South China Sea.
The report is based on the think tank's analysis on satellite images from January and February.
China's foreign and defense ministries did not respond to requests for comments, Reuters reported.
There were reports last week that China had installed missile batteries in the Paracel island chain, drawing criticism and concern from the US and Vietnam.
According to reports, China had deployed two batteries of eight surface-to-air missile launchers and a radar system on the Woody Island in the Paracel chain, which is claimed by China, Taiwan and Vietnam.
South China Sea Dispute
The overlapping claims of sovereignty over two island chains by China, Taiwan, Malaysia, the Philippines, Vietnam and Brunei has made the South China Seas a sensitive region. The United States has strategic interests in the region as well, and it offers a counter balance against Beijing's influence in the waters.
The US adopts a stern line against China's land reclamation, construction and militarisation in these islands but China staunchly defends its claim to sovereignty in the region.
The US too has US military facilities in Southeast Asia -- Philippines and Thailand. It also has stationed its Poseidon sub-hunters and electronic warfare platforms in Malaysia and Singapore.
The mostly uninhabited islands in South China Sea are of crucial strategic importance. The two major island chains -- the Paracels and the Spratlys -- are thought to harbour natural resources around them. China hopes the oil and natural gas reserves in the region could ensure its energy security.
The sea is also a major trading route through which ship-borne trade worth $5 trillion passes every year.
For energy hungry China the sea routes in South China Sea are crucial as most of its imported oil flows through these routes.
Control over the territory allows Beijing to prevent the US from expanding its sphere of influence in the region.