The USS Lassen's patrol was the most significant U.S. challenge yet to the 12-nautical-mile territorial limits China claims around artificial islands it has built up in the Spratly archipelago as Beijing exercises its growing maritime power. 

Washington's move followed months of deliberation by the administration of President Barack Obama and could ratchet up tension in one of the world's busiest shipping lanes and increase strains in U.S.-China relations.

A U.S. defense official said the Lassen also went within 12-mile limits of features in the disputed sea claimed by Vietnam and U.S. treaty ally, the Philippines. They said such "freedom-of-navigation" patrols were expected to become more frequent.