Tsai was speaking a day after she confirmed she would run for re-election in early 2020 despite falling ratings and an increasingly strained relationship with China.

Beijing still sees democratic Taiwan as part of its territory to be reunified, despite the two sides being ruled separately since the end of a civil war in 1949.

Tsai was responding to recent comments by Wu Den-yih, head of the main opposition Kuomintang (KMT), that his party would pursue a peace treaty with Beijing if it were to regain power next year.

"There would be no so-called negotiation on equal footing and no real peace as China refuses to give up the use of force against Taiwan and forcefully pushes the 'one country, two systems' framework," she said in a media briefing.

"China's military intentions and its refusal to give up the use of force against Taiwan is a real source of regional instability and a threat to regional peace," she added.

"One country, two systems" is China's proposal to absorb Taiwan into the mainland but allow it to keep some of its freedoms.

Beijing has made its dislike of Tsai and her independence-leaning Democratic Progressive Party clear.

After her election in 2016, it cut communication with her administration, stepped up military drills and poached several of Taiwan's dwindling diplomatic allies.

President Xi Jinping reiterated in a speech last month that China would not renounce the option of using military force to bring Taiwan into the fold, describing unification with the mainland as "inevitable".

A KMT win in 2020 would likely please leaders in Beijing given the much closer relationship it forged with the previous administration of Ma Ying-jeou.

Ma suggested in 2011 that Taiwan should consider a peace treaty with China within the coming decade, to formally bring an end to a civil war that has actually been over for seventy years.

The proposal sparked criticism from detractors that it would be tantamount to a unification or surrender treaty.

Ma later stressed that he would only move ahead for a peace agreement with the approval of both the parliament and the public, and the issue had been shelved since.

The KMT's drubbing at the 2016 election partly stemmed from voter unease over the party's perceived cosiness to the mainland.

But Wu -- a former vice president under Ma -- has resurrected the issue ahead of next year's polls. He is among the KMT bigwigs who have been tipped to run for president.

Tsai said she believed voters would balk at the proposal unless Beijing withdrew its threats.

"I believe Taiwanese society would not accept any political agreement that could harm or eliminate our sovereignty or eliminate Taiwan's democracy," she said.