US Secretary of State John Kerry on Wednesday slammed China for its increased "militarization" in the strategically important South China Sea, after Taiwan said Beijing deployed surface-to-air missiles on a disputed island there.

"There is every evidence, every day, that there has been an increase of militarization of one kind or another. It's of a serious concern," Kerry told reporters. "We had these conversations with the Chinese and I'm confident that over the next days, we will have further very serious conversations on this."