Taiwan's Defense Ministry said the missile batteries had been set up on Woody Island in the Paracels chain, which has been under Chinese control for decades but also is claimed by Taiwan and Vietnam.

A U.S. defence official also confirmed the "apparent deployment" of the missiles, first reported by Fox News.

"There is every evidence, every day that there has been an increase of militarization of one kind or another," Kerry told reporters when asked about the reported deployment. "It's of serious concern.

"We have had these conversations with the Chinese and I am confident that over the next days we will have further very serious conversation on this."

The United States claims no territory in the South China Sea but has expressed serious concerns about how China's increasingly assertive pursuit of territorial claims there could affect the vital global trade routes that pass though it.