The USS Lassen, a guided-missile destroyer, is nearing a 12-nautical-mile limit around artificial islands built by China in the South China Sea, and will be in the area for several hours, a U.S. defense official said on Monday.
The Navy patrol marks the start of a series of challenges to China's territorial claims in one of the world's busiest sea lanes.
The vessel began the journey early on Tuesday local time near Subi and Mischief reefs in the Spratly archipelago, features that were formerly submerged at high tide before China began a massive dredging project to turn them into islands in 2014.
The patrols mark the most serious U.S. challenge yet to the 12-nautical-mile territorial limit China claims around the islands and are certain to anger Beijing, which said last month it would "never allow any country" to violate its territorial waters and airspace in the Spratlys.
The ship would likely be accompanied by a U.S. Navy P-8A surveillance plane and possibly P-3 surveillance plane, which have been conducting regular surveillance missions in the region, according to the defense official, who spoke on condition of anonymity.
Additional patrols would follow in coming weeks and could also be conducted around features that Vietnam and the Philippines have built up in the Spratlys, the official said.
"This is something that will be a regular occurrence, not a one-off event," said the official. "It's not something that's unique to China."
White House spokesman Josh Earnest referred questions on any specific operations to the Pentagon but said the United States had made clear to China the importance of free flow of commerce in the South China Sea.