China is looking to add substantial military infrastructure in the islands in the South China Sea this year, the Pentagon has said.
The US Defense Department has estimated that China's reclamation work has added more than 3,200 acres (1,300 hectares) of land on seven features it occupies in the Spratly Islands in the space of two years.
The installation of surveillance systems will give China long-term "civil-military bases" in the disputed waters, the Pentagon said in a report on China's military activities in 2015 it submitted to Congress.
The report says China completed its major reclamation efforts in October after switching focus to infrastructure development that included three 9,800 foot-long (3,000 meter) airstrips with the space to accommodate advanced fighter jets.
"Additional substantial infrastructure, including communications and surveillance systems, is expected to be built on these features in the coming year. China will be able to use its reclaimed features as persistent civil-military bases to enhance its presence in the South China Sea significantly," the report says, according to Reuters.
The report has been published at a time of intense tension over the maritime claims by China and several nations in the region. Washington has accused Beijing of militarizing the South China Sea while Beijing, in turn, has criticized the increased US naval patrols and exercises in Asia.
The Pentagon report says China is focusing on developing capabilities to counter outside intervention in any conflict.
However, Beijing apparently tries to avoid any sort of direct confrontation with the United States in Asia, given the potential economic damage.
"China demonstrated a willingness to tolerate higher levels of tension in the pursuit of its interests, especially in pursuit of its territorial claims," the report says.
The report has also repeats the accusation that the Chinese government and military engage in cyber attacks on US government computer systems, a charge Beijing has denied.
"Targeted information could inform Chinese military planners' work to build a picture of U.S. defense networks, logistics, and related military capabilities that could be exploited during a crisis," the report said.