Subi, Mischief and Fiery Cross reefs.
A U.S. defense official told CNN that the destroyer USS Lassen "conducted a transit" within 12 nautical miles of Subi Reef in the Spratly Islands on Tuesday morning local time.
The operation put the ship within an area that would be considered Chinese sovereign territory if the U.S. recognized the man-made islands as being Chinese territory, the official added.
The mission, which had the approval of President Barack Obama, has now concluded, the official said.
The United States had not breached the 12-mile limit since China began massive dredging operations to turn three reefs into artificial islands in 2014.
| the guided missile destroyer USS Lassen |
(DDG 82) launches a BQM-74E drone
In May, a U.S. surveillance plane carrying a CNN crew swooped over the Spratly Islands, triggering eight warnings from the Chinese navy to back off.
Another defense official told CNN that the operation was "routine" and was in accordance with international law.