(Reuters) - US Defense Secretary Ash Carter on Tuesday (March 1) warned China against what he called "aggressive" actions in the South China Sea region, including the placement of surface-to-air missiles on a disputed island, and said they would have consequences.

"The United States joins virtually every nation in the region in being deeply concerned about the artificial island construction and militarisation in the South China Sea - including steps China has taken most recently by placing anti-access systems and military aircraft on a disputed island. These activities have the potential to increase the risk of miscalculation or conflict among claimant states," Mr Carter said.

During his remarks at a press conference in San Francisco, Mr Carter underscored the US military's determination to safeguard maritime security in the South China Sea region, which sees about 30 per cent of the world's trade transit its waters each year.

"China must not pursue militarisation in the South China Sea. Specific actions will have specific consequences. Indeed, while some in the region appear determined to play spoiler, the United States and our many friends in the region don't plan on letting anyone upend seven decades' worth of progress," Mr Carter said.

The United States has carried out several freedom of navigation exercises in the South China Sea recent months, sailing near disputed islands to underscore its rights to navigate the seas. US Navy officials say they plan to conduct more and increasingly complex exercises in the future.