The U.S. Navy sailed two ships through the Taiwan Strait on Wednesday, a move likely to upset China.
A destroyer and an oil ship made the journey.
This is the third time this year the Navy carried out what it calls a "routine transit."
"The ships' transit through the Taiwan Strait demonstrates the U.S. commitment to a free and open Indo-Pacific," the U.S. Pacific Fleet said in a statement. "The U.S. Navy will continue to fly, sail and operate anywhere international law allows."
A U.S. official told the French news agency, Agence France-Presse, that Chinese ships were standing by and monitoring the American vessels but that both sides acted in a manner that was "safe and professional."
China protested earlier sailings as a challenge to its sovereignty. It regards Taiwan as part of mainland China. It has threatened military action if Taiwan declares independence, although the island has ruled itself since the Communists seized power in China in 1949.
The U.S. is obliged to come to Taiwan's defense if it is ever attacked.