China has sent fighter jets to an island in the disputed Paracel island chain in South China Sea where it had deployed surface-to-air missile systems earlier this month.
Chinese Shenyang J-11 and Xian JH-7 warplanes were spotted on Woody Island over the past few days, FOX News reported, citing US officials.
The fighter sorties were reported even as a senior US commander said Beijing is "changing the operational landscape" in the South China Sea by its aggressive military actions.
China's recent deployment of missiles and a high frequency radar system in the disputed waters are part of its plans to militarily dominate East Asia, head of the US Pacific Command Admiral Harry Harris said.
"[China] is clearly militarising the South China (Sea). You'd have to believe in a flat Earth to think otherwise," Admiral Harris said, Reuters reported.
Reports last week that Beijing deployed two batteries of eight surface-to-air missile launchers and a radar system on Woody Island, which is claimed by China, Taiwan and Vietnam, had raised concerns over China's increasing 'militarisation' of the region.
US Pacific Command spokesman Darryn James confirmed the report but added that China often sends jets to Woody Island, which is under Beijing's control. The island has an active airfield since 1991 but it was upgraded recently to accommodate J-11 fighter.
"We are still concerned that the Chinese continue to put advanced arms systems on this disputed territory," he spokesman said.
Beijing confirmed deploying missile batteries on Woody island and defended its right to sovereignty in the region, which has been called into question by the US, which conducts 'freedom of navigation' operations.
China lays claim to Paracel and Spratly island chains in the South China Sea, stating that these were integral part of the empire from ages.
In 1947 China formalised the claims by issuing a map showing the islands in its territory. But Vietnam has contested China's claims saying its rule over Paracels and Spratlys dates back to the 17th century.
China scored decisive military victories over Vietnam in recent decades in its quest to cement claims over the island chains. In 1974, more than 70 Vietnamese soldiers died in China's military offensive that seized control of Paracels. In 1988 Vietnam lost Spratlys to China in another bloody military conflict.
China angered Vietnam and the Philippines in 2012 when it created Sansha city, making it the administrative headquarters for the Paracels. Again that year, Vietnam alleged China sabotaged its exploration operations, setting off massive anti-China protests in the country.
In 2014, China set up a drilling rig in waters near the Paracel Islands and in 2015 satellite images showed Beijing was building an airstrip on land reclaimed around the Spratlys.
More than 20 people were killed in popular protests in Vietnam after China's rig move. China withdrew the rig after conducting drilling for two months.