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.
Why are the United States and China frenemies?02:25
The United States hadn't breached the 12-mile limit since China began massive dredging operations to turn three reefs into artificial islands in 2014 -- even though maritime law doesn't usually accord territorial waters to islands built on previously submerged reefs.
Chinese government: Don't push us
On Tuesday, the Chinese Ministry of Foreign Affairs warned of consequences if a country caused trouble or raised tensions in the territories China claims as its own.
"If any country thinks that, through some gimmicks, they will be able to interfere with or even prevent China from engaging in reasonable, legitimate and legal activities in its own territories, I want to suggest those countries give up such fantasy," ministry spokesman Lu Kang said.
"In fact, if relevant parties insist on creating tensions in the region and making trouble out of nothing, it may force China to draw the conclusion that we need to strengthen and hasten the buildup of our relevant capabilities. I advise the U.S. not to create such a self-fulfilling prophecy."