The US sailed a navy warship through the Taiwan Strait on Wednesday showing support for the island's government and defying Chinese warnings about the self-ruled territory.
The US military announced the provocative manoeuvre hours after China said it was prepared for war over the issue of Taiwanese independence, Reuters reported.
Taiwan, which the US is legally committed to help defend, is only one point of friction between Washington and Beijing as they jostle for supremacy in the South China Sea.
Antietam, a guided-missile cruiser, passed through the strait to make a statement, a navy commander said.
"The transit through the Taiwan Strait demonstrates the US commitment to a free and open Indo-Pacific," said Cmdr Clay Doss, of the US Navy's Seventh Fleet.
"The US Navy will continue to fly, sail and operate anywhere international law allows."
The 180-kilometre wide Taiwan Strait is all that stands between China and Taiwan.
Since 1949, China and Taiwan have been at odds over which rival government can legitimately claim to rule the island, mainland China and their respective territories
China released a national defence document indicating that pro-independence, separatist forces in Taiwan, Xinjiang and Tibet were a threat to national security, CNN reported on Wednesday.
The white paper said that Taiwan’s push for independence meant China "must and will be reunited".
"If there are people who dare to try to split Taiwan from the country, China’s military will be ready to go to war to firmly safeguard national sovereignty, unity and territorial integrity," Chinese Defence Ministry spokesman Wu Qian said.
US-Chinese relations have become strained under President Donald Trump as the world’s two largest economic powers stand off over trade tariffs and sanctions.
The US regularly conducts patrols in the South China Sea.