The Chinese navy on Sunday kept a close watch as two American warships sailed through the Taiwan Strait, separating China and Taiwan, the first such operation since US House Speaker Nancy Pelosi visited Taipei early this month, sparking a new round of tensions between the two countries.

The US warships sailed through the Taiwan Strait where the Chinese military has carried out its biggest exercises for several days in August, often crossing the median line that separated the Chinese mainland and Taiwan, which Beijing viciously claims as part of it.

"The USS Antietam and the USS Chancellorsville, two US guided-missile cruisers, sailed through the Taiwan Strait on August 28 and hyped it up publicly, the Eastern Theatre Command (ETC) of the Chinese People's Liberation Army (PLA) said on Sunday.

The ETC conducted security tracking and monitoring of the US warships' passage in the whole course and had all movements of the two US warships under control, Senior Colonel Shi Yi, spokesperson for the ETC, said in a statement.

The troops of the PLA Eastern Theatre Command always stay on high alert and get ready to thwart any provocation, he added.

Criticising the American naval ships transit through the island, a write-up in the state-run Global Times said the US is trying to appease the Taiwan authorities and regional allies, conveying to them that Washington will not back down under military pressure from the Chinese mainland .

This is the first time the US warships sailed through the Taiwan Strait, a busy and strategic waterway separating China and Taiwan, after Pelosi's visit though according to the official media accounts here over 100 American warships transited through the water since 2012, challenging China's claims over the area.

The US has been conducting similar naval and aerial expeditions in the disputed South China Sea to assert freedom of navigation, countering Beijing's claims over most of the area.

The Philippines, Vietnam, Malaysia, Brunei and Taiwan have counterclaims over the South China Sea.

Pelosi's visit, the first by a top US official in 25 years, set off a series of US lawmakers visits to Taipei.

US Senator Marsha Blackburn became the fourth lawmaker to visit Taiwan when she travelled to Taipei last week.

"I will not be bullied by Communist China into turning my back on the island," she was quoted as saying by CNN.

"Taiwan is our strongest partner in the Indo-Pacific Region. Regular high-level visits to Taipei are long-standing US policy," said Blackburn, a Tennessee Republican who sits on the Senate Armed Services Committee.

Blackburn met Taiwanese President Tsai Ing-wen and other senior officials during her three-day stay, the Hong Kong-based South China Morning Post reported.

After Pelosi's visit, China went ballistic conducting massive military exercises for several days including firing missiles over the Taiwan island, sparking concerns that Beijing may be contemplating a military offensive.