Ms Tsai insisted that the sovereignty of the self-governing island was not in doubt or up for negotiation.
“We don’t have a need to declare ourselves an independent state,” the 63-year-old president told the BBC in an exclusive interview, her first since the election.
“We are an independent country already and we call ourselves the Republic of China, Taiwan.”
Such statements infuriate Beijing, which wants a return to the “One China” principle favoured by the main rival she saw off in the race for president, Han Kuo-yu from the Kuomintang party.
“The situation has changed,” she says. “The ambiguity can no longer serve the purposes it was intended to serve.”
And what has really changed, she suggests, is China.
“Because [for more than] three years we’re seeing China has been intensifying its threat… they have their military vessels and aircraft cruising around the island,” she says.
But she says she has shown restraint. She has, for example, stopped short of the formal declaration of independence – amending the constitution and changing the flag – that some in her Democratic Progressive Party would like.
China has said it would regard such a move as a pretext for military action.
“There are so many pressures, so much pressure here that we should go further,” she says.
“But [for] more than three years, we have been telling China that maintaining a status quo remains our policy… I think that is a very friendly gesture to China.”
“You cannot exclude the possibility of war at any time,” she says.
“But the thing is you have to get yourself prepared and develop the ability to defend yourself.”
And is Taiwan ready?
“We have been trying very hard and making a lot of efforts to strengthen our capability,” she replies.
“Invading Taiwan is something that is going to be very costly for China.”