The United States has positioned troops on a tiny island chain less than four miles from the Chinese coast, Taiwan has admitted.

In an apparent escalation of the American military presence in Taiwan, a Taiwanese defence minister told reporters the country was running an “exchange” with the US to “figure out how to improve” its military.

Although the US has announced it was training Taiwanese forces on the country’s main island, Formosa, the Pentagon has never acknowledged the presence of American troops on the Kinmen Islands, which lie 3.7 miles from the Chinese coastal city of Xiamen.

In response to reports that US special forces were operating on the islands, Chiu Kuo-cheng, the minister, admitted on Tuesday that his country’s military was learning from American forces there.

“This exchange is for mutual observation, to identify the problems we have, figure out how to improve and to recognise their strengths so we can learn from them,” he said.

He added: “We can learn from each other to see what strengths we have. This is a fixed thing.”

The Kinmen Islands sit on the far side of the Taiwan Strait, the 110-mile body of water that separates Taiwan and China. They are around 100 miles from Taiwan, but easily visible from the Chinese mainland.

Taiwan has stationed its own amphibious soldiers, known as “frogmen”, on both the Kinmen Islands and other outlying islands, amid concerns about a Chinese invasion that US officials have said could take place by 2027.

In recent months, China has stepped up military exercises in the Taiwan Strait and Communist Party officials have not ruled out occupying Taiwan with military force in the future.

On Thursday the Taiwanese government said nine Chinese aircraft had crossed the median line in the strait, prompting it to deploy “appropriate forces and assets in response to the detected activities”.

Air defence violations

Taiwan says its air defence identification zone (ADIZ) has been violated on a near-daily basis by Chinese aircraft as tensions have mounted.

Earlier this week, Taiwan said the country had constructed “enormous” bases on three islands nearby.

The admission that US forces are operating so close to China risks inflaming tensions between Washington and Beijing, which has long objected to the American military operating in the region.

In January, the Chinese government accused the US of “dangerous provocations” after a US naval destroyer sailed through the Taiwan Strait, in what was perceived as a show of force.

While the US does not support full political independence for Taiwan, the countries maintain informal diplomatic relations and Joe Biden has said that American forces would defend the country in the event of an invasion.

The row over Taiwan’s sovereignty is viewed by the US as part of its wider competition with China in the Indo-Pacific region.

A Pentagon spokesman refused to confirm reports of American troops on the outlying islands, telling the Wall Street Journal: “Our commitment to Taiwan is rock-solid and contributes to the maintenance of peace and stability across the Taiwan Strait and within the region.”