Self-governed Taiwan, which has never formally declared independence, lives under the constant threat of invasion by China, which views the island as its territory and has vowed to one day seize it, by force if necessary.

"Realising national reunification by peaceful means best serves the interests of the nation as a whole including our brethren in Taiwan," Xi said in a speech marking the 110th anniversary of a revolution that ended millennia of imperial rule and led to the founding of the Republic of China.

A large portrait of Sun Yat-sen, the western-educated doctor who founded the Republic of China, which remains the formal name of Taiwan, towered over the stage as Xi spoke.

Sun led the 1911 toppling of the Qing empire, seen as the forerunner to the eventual Communist revolution, making him one of the few figures revered on both sides of the Taiwan Strait.

"The complete reunification of our country will be and can be realised," Xi said.

He also warned against foreign interference in Taiwan after a Pentagon official confirmed US special operations forces have been quietly training Taiwanese troops for months.

"The Taiwan issue is purely China's internal affair and does not allow any external interference," he said.

"Nobody should underestimate the Chinese people's firm resolution, staunch will and formidable capacity to defend their national sovereignty and territorial integrity," he said.

- Increasing pressure -

Beijing has ramped up pressure on Taipei since the 2016 election of President Tsai Ing-wen, who views the island as "already independent".

"Taiwan independence is the biggest obstacle to the reunification of the motherland and a serious hidden danger," Xi warned. "Those who forget their origins, betray the motherland, or split the country never meet a good end, and will inevitably be spurned by the people and put on trial by history."

Tsai is scheduled to speak Sunday at an event commemorating the 1911 revolution, one of the few events that unite China and Taiwan.

Taiwan's defence minister said Wednesday that military tensions with China were at their highest in four decades, after around 150 Chinese warplanes -- a record number -- made incursions into Taiwan's air defence zone in recent days.

Xi's comments come after Britain last week sent a warship through the Taiwan Strait, challenging Beijing's claim to the sensitive waterway, and a French delegation visited Taiwan despite warnings from China.

On Friday, Chinese foreign ministry spokesman Zhao Lijian rebuked comments made by French delegation member Alain Richard, who referred to Taiwan as a "country" during a speech on Thursday.

Zhao said Richard, a former French defence minister, made the remarks "out of self-interest to undermine relations between China and France", adding that his use of the term "country" had "blatantly violated" international practice".