US intelligence services spotted Chinese Shenyang J-11 and Xian JH-7 warplanes on Woody Island in disputed Paracel Islands chain in the past few days, US media reports.
"China has deployed fighter jets to the same contested island in the South China Sea to which it also has sent surface-to-air missiles."
Woody Island, which is also claimed by Taiwan and Vietnam, has had an operational airfield since the 1990s but it was upgraded last year to accommodate the J-11.
“We are still concerned that the Chinese continue to put advanced arms systems on this disputed territory,” Cpt James said.
The move was reported as US secretary of state John Kerry hosted his Chinese counterpart, foreign minister Wang Yi, in Washington.
Last week, China confirmed it had placed “weapons” on Woody Island, defending what it said was its sovereign right to do so.