The election campaign, which is also for Taiwan’s legislature, has kicked into high gear, and is being closely watched by Taiwan’s giant neighbour China, which claims Taiwan as sacred Chinese territory, to be brought under its control by force if needed.

China on Sunday sailed an aircraft carrier group through the sensitive Taiwan Strait, the same day Tsai announced her running mate, former premier William Lai, who has angered Beijing with his pro-independence comments. Taiwan denounced the carrier sailing as attempt to intimidate voters.

China fears Tsai and her Democratic Progressive Party will push for Taiwan’s formal independence, a red line for Beijing which in 2005 enacted an “anti-secession law” that allows it to use force on Taiwan in extreme cases.

Tsai, speaking after formally registering to run for re-election in the Jan. 11 vote, said the vote was happening at a crucial time, as China’s pressure grows and against the backdrop of anti-government protests in Chinese-run Hong Kong.

“Our Republic of China, Taiwan, is a country, a sovereign, independent country. Our people have the right to choose their own president,” she told reporters, referring to Taiwan by its official name.

Asked whether she supported Taiwan independence, Tsai said the island already had sovereignty.

“We have sovereignty, we have a government, we have a democratic free system, we defend ourself, we have diplomatic relations. This is the Republic of China, Taiwan, that I’m talking about,” she said.

China’s attempts to involve itself in Taiwan’s election are “clear and easy to see” as they seek to damage the island’s democracy, Tsai added, when asked about the Chinese carrier group in the Taiwan Strait.

“As a large country, internationally and regionally they have to have a responsibility to maintain regional peace and stability,” she said.

Tsai declined direct comment on the Chinese carrier which she called an “individual case”.

“China intervening in Taiwan’s election is happening, and it’s happening every day.”

China described the carrier sailing as routine and not aimed at anyone in particular, dismissing Taiwan’s complaints.

China’s President Xi Jinping said in January that China reserved the right to use force to bring Taiwan under its control but will strive to achieve peaceful “reunification”.

Tsai is leading in the polls over her main opponent Han Kuo-yu of the China-friendly Kuomintang party.

Reporting by Ben Blanchard Editing by Robert Birsel.