China on Tuesday called on the United States to block the transit of Taiwanese president Tsai Ing-wen, who will stop over in the country en route to Paraguay and Belize.

Beijing views Taiwan as part of its own territory — to be reunified by force if necessary — and has stepped up military and diplomatic pressure since independence-leaning Tsai came to power in 2016.

Taiwan President Tsai Ing-wen. Photo: TaiwanGov.

Washington has diplomatically recognised Beijing over Taipei since 1979 but it remains a staunch military ally of Taiwan, a relationship that has long rankled the communist party leadership on the mainland.

At a regular press briefing on Tuesday, foreign ministry spokesman Geng Shuang urged Washington “not to allow the transit by the so-called Taiwan leader”.

“We have always been firmly opposed to any kind of such transit arranged in the US or other countries with diplomatic ties with China,” Geng said, adding that Beijing has “launched solemn representations to the US side” on the matter.

Tsai is set to stop over in Los Angeles and Houston during the trip set for August 12-20, Taiwanese officials said Monday.

Beijing bristles at any moves by countries that might lend Taiwan diplomatic support or legitimacy.

China reacted with alarm when President Donald Trump took a congratulatory phonecall from Tsai shortly after his 2016 election, the first time since 1979 that a US leader had spoken directly with their counterpart in Taiwan.

The new American Institute. Photo: TaiwanGov.

Last month the United States unveiled a new US$255 million de facto embassy in Taipei in what was hailed as a “milestone” in relations, drawing renewed ire from China.

During a visit to three Pacific allies last year, Tsai transitted through Hawaii and the US territory of Guam, prompting official protests from Beijing.

On next month’s trip, she is seeking to firm up ties with a dwindling number of foreign allies, many lured away by what the president has described as Beijing’s “dollar diplomacy”.

Burkina Faso and the Dominican Republic switched recognition to Beijing in May, leaving Taipei with only 18 diplomatic allies around the world.

Under pressure from Beijing, a growing number of international airlines and companies recently changed their website classifications of Taiwan to “Taiwan, China” or “Chinese Taipei”.