China has deployed a surface-to-air missile system on one of its contested islands in the South China Sea, a report said Tuesday just as President Barack Obama called for "tangible steps" to reduce tensions in the region.

Fox News said that images from civilian firm ImageSat International show two batteries of eight missile launchers and a radar system arrived within the past week on Woody Island, part of the Paracels chain.

A US warship last month sailed close to another island in the chain -- which is claimed by China, Taiwan and Vietnam -- in a gesture to assert freedom of navigation in the region which drew a quick protest from Beijing.

The report on the missile batteries came as Obama wrapped up a two-day Southeast Asian summit in California where leaders voiced concern over Beijing's military build-up in the strategic and resource-rich area.

"We discussed the need for tangible steps in the South China Sea to lower tensions," Obama said, calling for "a halt to further reclamation, new construction and militarization of disputed areas."

China's increasingly muscular actions in the vital waterway featured heavily at the Association of Southeast Asian Nations (ASEAN) talks at Sunnylands, a sprawling California desert retreat.

In a joint statement, Obama and the 10 ASEAN leaders demanded the "peaceful resolution" of a myriad of competing territorial claims over islands, atolls and reefs.

Obama has tried to muster an informal coalition of Pacific allies to demand that Beijing respect the rule of law, hoping that China will want to avoid being painted as a regional bully.