WASHINGTON (AFP) - Two US warships sailed through the Taiwan Strait on Monday (Oct 22), a military spokesman said, in a move bound to aggravate China amid heightened tensions with Beijing.

The USS Curtis Wilbur and USS Antietam conducted a routine transit to demonstrate US commitment "to a free and open Indo-Pacific," Colonel Rob Manning told reporters at a press briefing.

It was the second time in the space of three months that American warships have conducted so-called "freedom of navigation" exercises in the 180-km wide stretch of water.

Multiple Chinese warships shadowed the two US vessels during the transit, following at a safe distance, defence officials told CNN.

China still sees Taiwan as part of its territory to be reunified, despite the two sides being ruled separately since the end of a civil war on the mainland in 1949.

Beijing recently conducted a series of military maneuvers, including a live fire exercise in the Taiwan Strait in April, declaring its willingness to confront Taiwan's "independence forces".

Washington remains Taipei's most powerful unofficial ally and its main arms supplier despite switching diplomatic recognition to Beijing in 1979.

The Trump administration has sought closer ties to the island, announcing plans last month to sell the island $330 million spare parts for several aircraft including the F-16 fighter and the C-130 cargo plane.

Taiwan's premier William Lai said during a parliamentary session on Tuesday that Taiwan respected the US right of passage in international waters and recognised "the various efforts of the US in maintaining peace in the Asia-Pacific Region".

Taiwan's defence ministry had said in an earlier statement that the military was "closely monitoring the US warships during their passage".