A small number of US forces are in Taiwan to train with Taiwanese soldiers, President Tsai Ing-wen said in an interview with CNN, confirming the presence of US troops on the self-governing island that China considers its own.

Tensions between Taiwan and China, which has not ruled out taking the island by force, have escalated in recent weeks as Beijing raises military and political pressure.

"We have a wide range of cooperation with the US aiming at increasing our defence capability," Tsai told CNN in the interview aired on Thursday.

Asked how many US service members are deployed in Taiwan, she said only that it was "not as many as people thought".

The confirmation comes as China is sharply increasing military pressure on Taiwan, including repeated missions by Chinese warplanes in Taiwan's air defence identification zone.

"Taiwan independence is a dead end, and there will also be no turning back for those who support it," China's foreign ministry spokesman Wang Wenbin said when asked about Tsai's comments.

"The US should abide by the One China Principle...and not whatever thing it concocts up itself unilaterally," he said, adding that the United States should cease military and official interactions with Taiwan.

While several Taiwan and international media outlets, including Reuters, have previously reported such training with US troops, official confirmation could further aggravate US-China relations at a time when Beijing is carrying out military exercises near Taiwan.

Asked about Tsai's comment, Taiwan Defence Minister Chiu Kuo-cheng told reporters Taiwan-US military interactions were "quite a lot and quite frequent" and had been going on for a long time.

"During these exchanges, any topic can be discussed," he said, adding that Tsai did not say that US forces are permanently based, or garrisoned, in Taiwan, in response to lawmaker questions that if they were then this could be a pretext for China to attack the island.

"There is no connection between personnel exchanges and the stationing of troops," Chiu said.

The United States withdrew its permanently based forces in Taiwan when it severed diplomatic ties with Taipei in favour of Beijing in 1979.

The United States, like most countries, has no formal diplomatic ties with Taiwan but is its most important international ally and main arms supplier. Taiwan sends its F-16 pilots to be trained at Luke Air Force Base in Arizona.

Tsai has said Taiwan is an independent country and repeatedly vowed to defend its democracy and freedom.