Taiwan's defense ministry on Monday said two U.S. warships sailed through the Taiwan Strait over the weekend, a move likely to heighten tension with Beijing.
The ships sailed from the south to the north through the waterway that divides Taiwan from mainland China, the ministry said.
Beijing frequently objects to the movement of foreign military vessels through the contest area on its claim to Taiwan as its own territory to be annexed by force if necessary.
Last week, Beijing complained to France after a French warship entered Chinese territorial waters while traversing the Taiwan Strait, and blamed British naval activity in the South China Sea for a downturn in bilateral relations.
Taiwan's defense ministry said in a statement that U.S. ships were free to sail through the Taiwan Strait as part of their "strategic Indo-Pacific tasks." Despite the lack of formal diplomatic ties, Taiwan is a key U.S. ally and provider of defensive weapons.
China has been increasingly willing to protest actions by foreign militaries in areas it considers its home waters or sphere of influence. That especially applies to the Taiwan Strait and South China Sea, which China claims almost in its entirety.
--The Associated Press contributed to this report.