At least two US warships sailed through the Taiwan Strait on Monday in an unexpected act that flies in the face of largely placid relations between China and Taiwan in recent months.

The Arleigh Burke-class guided-missile destroyer Stethem and navy cargo and ammunition ship Cesar Chavez passed through the 300-kilometer waterway separating mainland China and the self-ruled island of Taiwan on Monday and left the region in the early hours of Tuesday. In a statement, Taiwan’s Defense Ministry said it was fully aware of the ships’ operation in the strait.

The 8,900-ton Stethem is equipped with vertical launching systems for Tomahawk missiles as well as extensive sonar and radar systems, and it operates throughout the Pacific Ocean. In July 2017 it sailed within 12 nautical miles of the China-controlled Triton Island, the most southwestern of the Paracel Islands, in the South China Sea while conducting freedom of navigation exercises.

The supply/support vessel Cesar Chavez boasts a displacement of 41,000 tons and can haul 6,000 tons of cargo and more than 2,300 tons of fuel.

A file photo of the US cargo and ammunition ship Cesar Chavez. Photo: US Navy

The two vessels are under the command of the US Pacific Fleet headquartered in Pearl Harbor, Hawaii. The fleet said in a statement that “the ships’ transit through the Taiwan Strait demonstrates the US’ commitment to a free and open Indo-Pacific.”

The passage also came a day after US President Donald Trump announced he would postpone further punitive tariff rises on US$200 billion worth of Chinese exports to the US, acknowledging progress being made during the marathon trade talks between the two superpowers.

This is the fifth such strait transit by US warships in the last eight months.

The US has no formal ties with Taiwan, but is bound by law to help defend the island and is its main source of arms. Washington has sold Taiwan more than $15 billion worth of weaponry since 2010, according to the US Defense Department.