Defense Secretary Jim Mattis says the U.S. will continue to confront China's militarization of manmade islands in the South China Sea.

Mattis says Beijing hasn't abided by its promise not to put weapons on the Spratly Islands.

He says American ships are maintaining a "steady drumbeat" of naval operations around disputed islands, and "only one country" seems to be bothered by the vessels' activities.

Mattis says the U.S will confront "what we believe is out of step with international law."

During the weekend, two U.S. warships sailed close to the Paracel Islands, north of the Spratlys, drawing protests from China.

Mattis spoke to reporters traveling with him to a national security conference in Singapore.

He is stopping in Hawaii to mark a change in leadership at U.S. Pacific Command.