China is building a concrete runway on a disputed island in the South China Sea that will be capable of handling military aircraft when finished, satellite images released on Thursday showed.
Satellite images taken last month show a section of the runway across the Fiery Cross Reef, part of the Spratly Islands, an archipelago claimed by at least three other countries, including the Philippines, Vietnam and Taiwan.
The island building programme in the South China Sea may result in China gaining control of some of the world's most important waterways, the US's most senior military commander for Asia said.
''If this activity continues at pace, is that it - those would give them de facto control'' of the maritime territory they claim, Admiral Samuel Locklear, head of the US Pacific Command, told the US Senate.
Locklear said China could install long-range detection radars, base warships and warplanes on the islands, potentially giving it the ability to enforce an air defence identification zone.
It would also help China to locate a maritime security force in the waters that would be larger than the combined coast guards of the Southeast Asian countries, he said.
President Barack Obama said last week that the US is concerned that China is using its ''muscle and power'' to dominate smaller countries in the region.
China claims about four-fifths of the South China Sea, home to some of the world's busiest shipping lanes, under a so-called nine-dash line drawn on a 1940s map. China also claims a right to carry out construction work on its sovereign territory in the South China Sea.
Vietnam, the Philippines, Taiwan, Malaysia and Brunei also claim territory in the waters.
Joint efforts by the Association of Southeast Asian Nations to work with China to develop a code of conduct in the South China Sea did not help.
To help improve security in the region, the US had developed partnerships with nations that it wouldn't have considered possible over the past two decades, he said, citing Vietnam, Malaysia and Indonesia.
Locklear estimated that of the 300 submarines in the world that aren't US vessels, 200 are in the Indo-Pacific, which he said was the ''most militarized part of the world.''