Story highlights Images appear to show new airstrip being built in South China Sea

China had said that land reclamation almost complete

Chinese President Xi Jinping will visit U.S. next week

Hong Kong (CNN) China appears to building a third airstrip in disputed waters in the South China Sea, according to new satellite images analyzed by the Washington-based Center for Strategic and International Studies (CSIS).

The images, taken September 8, come after China pledged to bring land reclamation in those waters to a halt, and will make for uncomfortable discussions when Chinese President Xi Jinping visits Washington next week.

Greg Poling, the director of CSIS's Asia Maritime Transparency Initiative , said that China had reclaimed a flat rectangle of land with a retaining wall about 3,000 meters (3,280 yards) in length on Mischief Reef. It's similar to airstrips that China has been building on artificial islands at the Fiery Cross and Subi reefs in the contested Spratly Islands.

"If it does turn out to be a runway, China will have three airstrips that can carry any plane the PLA (People's Liberation Army) has to offer," he said.

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"All of these places have gone from being outposts on stilts to full islands, potentially with airstrips, within the space of a year or just over a year," he added.