Recent satellite photos show that China is building an airstrip on reclaimed land in a disputed part of the South China Sea, and could be planning another.
Jane's Defense Weekly said that images, dated March 23, from Airbus Defense and Space showed work on a runway on Fiery Cross Reef in the Spratly Islands, territory also claimed by several neighbors, including Vietnam, Taiwan and the Philippines.
Images of Fiery Cross Reef showed a paved section of runway 505 meters (552 yards) by 53 meters (58 yards) on the northeastern side of the reef, which China began turning into an island with extensive dredging last year, the report said.
Preparation of other runway sections had also begun further along the island and workers had paved an apron area of about 400 meters (437 yards) by 20 meters (22 yards).
The report said Fiery Cross was capable of housing a runway about 3,000 meters, well within the parameters of Chinese air force runways.
It said the photos showed further dredging work on the southwestern side of the island and floating cranes consolidating a harbor.
Other imagery taken in March indicates China could be building another artificial island big enough to house an airstrip capable of civilian and military use.
Beijing has repeatedly rejected criticism of the reclamation work, claiming that China has sovereign rights in the area.
Earlier this week, satellite pictures showed that China is also expanding two islands in the Paracel Islands, which are claimed by Vietnam.
The U.S. on Tuesday called on China to pursue peaceful solutions to territorial disputes in the South China Sea.
Also this week, Admiral Samuel Locklear, the head of the U.S. Pacific Command told U.S. lawmakers that the Chinese are "showing no slowdown in the pace of their military modernization, particularly in the navy," increasing the country's clout in the South and East China Seas.
Last week, the United States warned against militarization of contested territory in Asia and President Barack Obama accused China of using its "sheer size and muscle" to push around smaller nations after Beijing sketched out plans to use the Spratlys for military defense as well as to provide civilian services that would benefit other countries.
Speaking at an seminar in Washington on Thursday, China's ambassador to the United States, Cui Tiankai, said it was "natural" the work would include military defense facilities.
He said there "should be no illusion that anyone could impose on China a unilateral status quo" or "repeatedly violate China's sovereignty without consequences."
In an apparent reference to U.S. air activity, Cui added that the U.N. Convention on Law of the Sea, to which the United States is not a signatory, did not give anyone the right to "conduct intensive and close-range reconnaissance in other countries' exclusive economic zone."
The United States said it does not take sides in the South China Sea but has called for a freeze on provocative acts.
China claims most of the potentially energy-rich sea, through which $5 trillion of maritime trade passes every year. Western and Asian naval officials have expressed fears that China could try to limit both sea and air navigation once its reclaimed islands are fully established.
Some material for this report came from Reuters.