The Asia Maritime Transparency Initiative (AMTI) released satellite photos showing that Chinese warplanes can be launched from the Fiery Cross, Subi and Mischief Reefs in the Spratly Islands.
AMTI is part of the Center for Strategic and International Studies based in Washington. The institute is an American think tank and is responsible for U.S. military intelligence.
The photos showed that China has built naval, air, radar and defensive facilities. There is now a newly constructed satellite antenna on Fiery Cross in Subi.
The photos show hardened shelters with retractable roofs for mobile missile launchers at Fiery Cross, Subi and Mischief Reefs. There are hangars at Fiery Cross for 24 combat aircraft and three larger Chinese warplanes, including bombers.
AMTI also revealed that China installed HQ-9 surface-to-air missiles on Woody Island more than a year ago. The missile was deployed on at least one occasion.
China has repeatedly denied that it is constructing military facilities in the Spratly Islands. Chinese Premier Li Keqiang said that the activities in the South China Sea are a mere installation of defense equipment for "freedom of navigation."
Foreign spokesperson Hua Chunying said, "As for China deploying or not deploying necessary territorial defensive facilities on its own territory, this is a matter that is within the scope of Chinese sovereignty."
The spokesperson stressed that the South China Sea is part of China's territory.
Gary Ross, a spokesperson from the Pentagon, refused to comment on the issue. He said that the military will not elaborate on the results of its intelligence.
Ross said, "China's continued construction in the South China Sea is part of a growing body of evidence that they continue to take unilateral actions which are increasing tensions in the region and are counterproductive to the peaceful resolution of disputes."
U.S. Secretary of State Rex Tillerson said that China should not conduct military operations in the disputed waters.